diff --git a/src/Modal.tsx b/src/Modal.tsx
index cd6c6a3255..e2873783ea 100644
--- a/src/Modal.tsx
+++ b/src/Modal.tsx
@@ -10,7 +10,6 @@ Please see LICENSE files in the repository root for full details.
 import React, { StrictMode } from "react";
 import { createRoot, type Root } from "react-dom/client";
 import classNames from "classnames";
-import { type IDeferred, defer } from "matrix-js-sdk/src/utils";
 import { TypedEventEmitter } from "matrix-js-sdk/src/matrix";
 import { Glass, TooltipProvider } from "@vector-im/compound-web";
 
@@ -70,7 +69,7 @@ export interface IModal<C extends ComponentType> {
     /** A deferred to resolve when the dialog closes, with the results as provided by
      * the call to {@link close} (normally from the `onFinished` callback).
      */
-    deferred?: IDeferred<OnFinishedParams<C> | []>;
+    deferred?: PromiseWithResolvers<OnFinishedParams<C> | []>;
 }
 
 /** The result of {@link Modal.createDialog}.
@@ -254,7 +253,7 @@ export class ModalManager extends TypedEventEmitter<ModalManagerEvent, HandlerMa
     }
 
     private getCloseFn<C extends ComponentType>(modal: IModal<C>): [IHandle<C>["close"], IHandle<C>["finished"]] {
-        modal.deferred = defer<OnFinishedParams<C> | []>();
+        modal.deferred = Promise.withResolvers<OnFinishedParams<C> | []>();
         return [
             async (...args: OnFinishedParams<C>): Promise<void> => {
                 if (modal.beforeClosePromise) {
diff --git a/src/SlidingSyncManager.ts b/src/SlidingSyncManager.ts
index 88b839312d..815e438da7 100644
--- a/src/SlidingSyncManager.ts
+++ b/src/SlidingSyncManager.ts
@@ -49,7 +49,7 @@ import {
     SlidingSyncState,
 } from "matrix-js-sdk/src/sliding-sync";
 import { logger } from "matrix-js-sdk/src/logger";
-import { defer, sleep } from "matrix-js-sdk/src/utils";
+import { sleep } from "matrix-js-sdk/src/utils";
 
 // how long to long poll for
 const SLIDING_SYNC_TIMEOUT_MS = 20 * 1000;
@@ -184,7 +184,7 @@ export class SlidingSyncManager {
     public slidingSync?: SlidingSync;
     private client?: MatrixClient;
 
-    private configureDefer = defer<void>();
+    private configureDefer = Promise.withResolvers<void>();
 
     public static get instance(): SlidingSyncManager {
         return SlidingSyncManager.internalInstance;
diff --git a/src/WorkerManager.ts b/src/WorkerManager.ts
index a8a95ca727..1d403be88c 100644
--- a/src/WorkerManager.ts
+++ b/src/WorkerManager.ts
@@ -6,14 +6,12 @@ SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Com
 Please see LICENSE files in the repository root for full details.
 */
 
-import { defer, type IDeferred } from "matrix-js-sdk/src/utils";
-
 import { type WorkerPayload } from "./workers/worker";
 
 export class WorkerManager<Request extends object, Response> {
     private readonly worker: Worker;
     private seq = 0;
-    private pendingDeferredMap = new Map<number, IDeferred<Response>>();
+    private pendingDeferredMap = new Map<number, PromiseWithResolvers<Response>>();
 
     public constructor(worker: Worker) {
         this.worker = worker;
@@ -30,7 +28,7 @@ export class WorkerManager<Request extends object, Response> {
 
     public call(request: Request): Promise<Response> {
         const seq = this.seq++;
-        const deferred = defer<Response>();
+        const deferred = Promise.withResolvers<Response>();
         this.pendingDeferredMap.set(seq, deferred);
         this.worker.postMessage({ seq, ...request });
         return deferred.promise;
diff --git a/src/audio/Playback.ts b/src/audio/Playback.ts
index 58b8a23c22..5247e4836c 100644
--- a/src/audio/Playback.ts
+++ b/src/audio/Playback.ts
@@ -9,7 +9,6 @@ Please see LICENSE files in the repository root for full details.
 import EventEmitter from "events";
 import { SimpleObservable } from "matrix-widget-api";
 import { logger } from "matrix-js-sdk/src/logger";
-import { defer } from "matrix-js-sdk/src/utils";
 
 import { UPDATE_EVENT } from "../stores/AsyncStore";
 import { arrayFastResample } from "../utils/arrays";
@@ -158,7 +157,7 @@ export class Playback extends EventEmitter implements IDestroyable, PlaybackInte
             // 5mb
             logger.log("Audio file too large: processing through <audio /> element");
             this.element = document.createElement("AUDIO") as HTMLAudioElement;
-            const deferred = defer<unknown>();
+            const deferred = Promise.withResolvers<unknown>();
             this.element.onloadeddata = deferred.resolve;
             this.element.onerror = deferred.reject;
             this.element.src = URL.createObjectURL(new Blob([this.buf]));
diff --git a/src/components/structures/MatrixChat.tsx b/src/components/structures/MatrixChat.tsx
index 02a3a55c59..761b7cf0e0 100644
--- a/src/components/structures/MatrixChat.tsx
+++ b/src/components/structures/MatrixChat.tsx
@@ -19,7 +19,7 @@ import {
     type SyncStateData,
     type TimelineEvents,
 } from "matrix-js-sdk/src/matrix";
-import { defer, type IDeferred, type QueryDict } from "matrix-js-sdk/src/utils";
+import { type QueryDict } from "matrix-js-sdk/src/utils";
 import { logger } from "matrix-js-sdk/src/logger";
 import { throttle } from "lodash";
 import { CryptoEvent, type KeyBackupInfo } from "matrix-js-sdk/src/crypto-api";
@@ -215,7 +215,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
     };
 
     private firstSyncComplete = false;
-    private firstSyncPromise: IDeferred<void>;
+    private firstSyncPromise: PromiseWithResolvers<void>;
 
     private screenAfterLogin?: IScreen;
     private tokenLogin?: boolean;
@@ -254,7 +254,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
 
         // Used by _viewRoom before getting state from sync
         this.firstSyncComplete = false;
-        this.firstSyncPromise = defer();
+        this.firstSyncPromise = Promise.withResolvers();
 
         if (this.props.config.sync_timeline_limit) {
             MatrixClientPeg.opts.initialSyncLimit = this.props.config.sync_timeline_limit;
@@ -1471,11 +1471,11 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         // since we're about to start the client and therefore about to do the first sync
         // We resolve the existing promise with the new one to update any existing listeners
         if (!this.firstSyncComplete) {
-            const firstSyncPromise = defer<void>();
+            const firstSyncPromise = Promise.withResolvers<void>();
             this.firstSyncPromise.resolve(firstSyncPromise.promise);
             this.firstSyncPromise = firstSyncPromise;
         } else {
-            this.firstSyncPromise = defer();
+            this.firstSyncPromise = Promise.withResolvers();
         }
         this.firstSyncComplete = false;
         const cli = MatrixClientPeg.safeGet();
diff --git a/src/components/views/dialogs/MessageEditHistoryDialog.tsx b/src/components/views/dialogs/MessageEditHistoryDialog.tsx
index b4850130db..72b11bc4e1 100644
--- a/src/components/views/dialogs/MessageEditHistoryDialog.tsx
+++ b/src/components/views/dialogs/MessageEditHistoryDialog.tsx
@@ -8,7 +8,6 @@ Please see LICENSE files in the repository root for full details.
 
 import React, { type JSX } from "react";
 import { type MatrixEvent, EventType, RelationType, type MatrixClient, MatrixError } from "matrix-js-sdk/src/matrix";
-import { defer } from "matrix-js-sdk/src/utils";
 import { logger } from "matrix-js-sdk/src/logger";
 
 import { MatrixClientPeg } from "../../../MatrixClientPeg";
@@ -58,7 +57,7 @@ export default class MessageEditHistoryDialog extends React.PureComponent<IProps
         const eventId = this.props.mxEvent.getId()!;
         const client = MatrixClientPeg.safeGet();
 
-        const { resolve, reject, promise } = defer<boolean>();
+        const { resolve, reject, promise } = Promise.withResolvers<boolean>();
         let result: Awaited<ReturnType<MatrixClient["relations"]>>;
 
         try {
diff --git a/src/components/views/rooms/Autocomplete.tsx b/src/components/views/rooms/Autocomplete.tsx
index 31d32da53c..a7a211e828 100644
--- a/src/components/views/rooms/Autocomplete.tsx
+++ b/src/components/views/rooms/Autocomplete.tsx
@@ -10,7 +10,6 @@ import React, { createRef, type RefObject } from "react";
 import classNames from "classnames";
 import { flatMap } from "lodash";
 import { type Room } from "matrix-js-sdk/src/matrix";
-import { defer } from "matrix-js-sdk/src/utils";
 
 import Autocompleter, {
     type ICompletion,
@@ -177,7 +176,7 @@ export default class Autocomplete extends React.PureComponent<IProps, IState> {
             }
         }
 
-        const deferred = defer<void>();
+        const deferred = Promise.withResolvers<void>();
         this.setState(
             {
                 completions,
diff --git a/src/components/views/settings/tabs/user/SessionManagerTab.tsx b/src/components/views/settings/tabs/user/SessionManagerTab.tsx
index 262f788daa..ab5b941cde 100644
--- a/src/components/views/settings/tabs/user/SessionManagerTab.tsx
+++ b/src/components/views/settings/tabs/user/SessionManagerTab.tsx
@@ -9,7 +9,6 @@ Please see LICENSE files in the repository root for full details.
 import React, { lazy, Suspense, useCallback, useContext, useEffect, useRef, useState } from "react";
 import { type MatrixClient } from "matrix-js-sdk/src/matrix";
 import { logger } from "matrix-js-sdk/src/logger";
-import { defer } from "matrix-js-sdk/src/utils";
 
 import { _t } from "../../../../../languageHandler";
 import Modal from "../../../../../Modal";
@@ -98,7 +97,7 @@ const useSignOut = (
                 const url = getManageDeviceUrl(delegatedAuthAccountUrl, deviceId);
                 window.open(url, "_blank");
             } else {
-                const deferredSuccess = defer<boolean>();
+                const deferredSuccess = Promise.withResolvers<boolean>();
                 await deleteDevicesWithInteractiveAuth(matrixClient, deviceIds, async (success) => {
                     deferredSuccess.resolve(!!success);
                 });
diff --git a/src/settings/handlers/AccountSettingsHandler.ts b/src/settings/handlers/AccountSettingsHandler.ts
index 3536169c59..3ea9db158e 100644
--- a/src/settings/handlers/AccountSettingsHandler.ts
+++ b/src/settings/handlers/AccountSettingsHandler.ts
@@ -8,7 +8,6 @@ Please see LICENSE files in the repository root for full details.
 */
 
 import { type AccountDataEvents, ClientEvent, type MatrixClient, type MatrixEvent } from "matrix-js-sdk/src/matrix";
-import { defer } from "matrix-js-sdk/src/utils";
 import { isEqual } from "lodash";
 
 import MatrixClientBackedSettingsHandler from "./MatrixClientBackedSettingsHandler";
@@ -162,7 +161,7 @@ export default class AccountSettingsHandler extends MatrixClientBackedSettingsHa
 
         // Attach a deferred *before* setting the account data to ensure we catch any requests
         // which race between different lines.
-        const deferred = defer<void>();
+        const deferred = Promise.withResolvers<void>();
         const handler = (event: MatrixEvent): void => {
             if (event.getType() !== eventType || !isEqual(event.getContent<AccountDataEvents[K]>()[field], value))
                 return;
diff --git a/src/settings/handlers/RoomAccountSettingsHandler.ts b/src/settings/handlers/RoomAccountSettingsHandler.ts
index e98cb3725d..8fdf412adf 100644
--- a/src/settings/handlers/RoomAccountSettingsHandler.ts
+++ b/src/settings/handlers/RoomAccountSettingsHandler.ts
@@ -8,7 +8,6 @@ Please see LICENSE files in the repository root for full details.
 */
 
 import { type MatrixClient, type MatrixEvent, type Room, RoomEvent } from "matrix-js-sdk/src/matrix";
-import { defer } from "matrix-js-sdk/src/utils";
 
 import MatrixClientBackedSettingsHandler from "./MatrixClientBackedSettingsHandler";
 import { objectClone, objectKeyChanges } from "../../utils/objects";
@@ -99,7 +98,7 @@ export default class RoomAccountSettingsHandler extends MatrixClientBackedSettin
 
         await this.client.setRoomAccountData(roomId, eventType, content);
 
-        const deferred = defer<void>();
+        const deferred = Promise.withResolvers<void>();
         const handler = (event: MatrixEvent, room: Room): void => {
             if (room.roomId !== roomId || event.getType() !== eventType) return;
             if (field !== null && event.getContent()[field] !== value) return;
diff --git a/src/settings/handlers/RoomSettingsHandler.ts b/src/settings/handlers/RoomSettingsHandler.ts
index c574ea1ea4..a31ccb87e9 100644
--- a/src/settings/handlers/RoomSettingsHandler.ts
+++ b/src/settings/handlers/RoomSettingsHandler.ts
@@ -14,7 +14,6 @@ import {
     RoomStateEvent,
     type StateEvents,
 } from "matrix-js-sdk/src/matrix";
-import { defer } from "matrix-js-sdk/src/utils";
 
 import MatrixClientBackedSettingsHandler from "./MatrixClientBackedSettingsHandler";
 import { objectClone, objectKeyChanges } from "../../utils/objects";
@@ -98,7 +97,7 @@ export default class RoomSettingsHandler extends MatrixClientBackedSettingsHandl
 
         const { event_id: eventId } = await this.client.sendStateEvent(roomId, eventType, content);
 
-        const deferred = defer<void>();
+        const deferred = Promise.withResolvers<void>();
         const handler = (event: MatrixEvent): void => {
             if (event.getId() !== eventId) return;
             this.client.off(RoomStateEvent.Events, handler);
diff --git a/src/stores/spaces/SpaceStore.ts b/src/stores/spaces/SpaceStore.ts
index ac4ffdaf0c..015c9fa0fd 100644
--- a/src/stores/spaces/SpaceStore.ts
+++ b/src/stores/spaces/SpaceStore.ts
@@ -21,7 +21,6 @@ import {
 } from "matrix-js-sdk/src/matrix";
 import { KnownMembership } from "matrix-js-sdk/src/types";
 import { logger } from "matrix-js-sdk/src/logger";
-import { defer } from "matrix-js-sdk/src/utils";
 
 import { AsyncStoreWithClient } from "../AsyncStoreWithClient";
 import defaultDispatcher from "../../dispatcher/dispatcher";
@@ -153,7 +152,7 @@ export class SpaceStoreClass extends AsyncStoreWithClient<EmptyObject> {
     private _enabledMetaSpaces: MetaSpace[] = [];
     /** Whether the feature flag is set for MSC3946 */
     private _msc3946ProcessDynamicPredecessor: boolean = SettingsStore.getValue("feature_dynamic_room_predecessors");
-    private _storeReadyDeferred = defer();
+    private _storeReadyDeferred = Promise.withResolvers<void>();
 
     public constructor() {
         super(defaultDispatcher, {});
diff --git a/src/utils/MultiInviter.ts b/src/utils/MultiInviter.ts
index 4f5bda879d..f8310de8bd 100644
--- a/src/utils/MultiInviter.ts
+++ b/src/utils/MultiInviter.ts
@@ -8,7 +8,6 @@ Please see LICENSE files in the repository root for full details.
 
 import { MatrixError, type MatrixClient, EventType, type EmptyObject } from "matrix-js-sdk/src/matrix";
 import { KnownMembership } from "matrix-js-sdk/src/types";
-import { defer, type IDeferred } from "matrix-js-sdk/src/utils";
 import { logger } from "matrix-js-sdk/src/logger";
 
 import { AddressType, getAddressType } from "../UserAddress";
@@ -51,7 +50,7 @@ export default class MultiInviter {
     private _fatal = false;
     private completionStates: CompletionStates = {}; // State of each address (invited or error)
     private errors: Record<string, IError> = {}; // { address: {errorText, errcode} }
-    private deferred: IDeferred<CompletionStates> | null = null;
+    private deferred: PromiseWithResolvers<CompletionStates> | null = null;
     private reason: string | undefined;
 
     /**
@@ -93,7 +92,7 @@ export default class MultiInviter {
                 };
             }
         }
-        this.deferred = defer<CompletionStates>();
+        this.deferred = Promise.withResolvers<CompletionStates>();
         this.inviteMore(0);
 
         return this.deferred.promise;
diff --git a/src/utils/Timer.ts b/src/utils/Timer.ts
index 6b120fa30a..c5d9084c31 100644
--- a/src/utils/Timer.ts
+++ b/src/utils/Timer.ts
@@ -6,8 +6,6 @@ SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Com
 Please see LICENSE files in the repository root for full details.
 */
 
-import { type IDeferred, defer } from "matrix-js-sdk/src/utils";
-
 /**
 A countdown timer, exposing a promise api.
 A timer starts in a non-started state,
@@ -22,7 +20,7 @@ a new one through `clone()` or `cloneIfRun()`.
 export default class Timer {
     private timerHandle?: number;
     private startTs?: number;
-    private deferred!: IDeferred<void>;
+    private deferred!: PromiseWithResolvers<void>;
 
     public constructor(private timeout: number) {
         this.setNotStarted();
@@ -31,7 +29,7 @@ export default class Timer {
     private setNotStarted(): void {
         this.timerHandle = undefined;
         this.startTs = undefined;
-        this.deferred = defer();
+        this.deferred = Promise.withResolvers();
         this.deferred.promise = this.deferred.promise.finally(() => {
             this.timerHandle = undefined;
         });
diff --git a/src/utils/exportUtils/HtmlExport.tsx b/src/utils/exportUtils/HtmlExport.tsx
index 6a75e8b222..c20ea8762f 100644
--- a/src/utils/exportUtils/HtmlExport.tsx
+++ b/src/utils/exportUtils/HtmlExport.tsx
@@ -13,7 +13,6 @@ import { renderToStaticMarkup } from "react-dom/server";
 import { logger } from "matrix-js-sdk/src/logger";
 import escapeHtml from "escape-html";
 import { TooltipProvider } from "@vector-im/compound-web";
-import { defer } from "matrix-js-sdk/src/utils";
 
 import Exporter from "./Exporter";
 import { mediaFromMxc } from "../../customisations/Media";
@@ -302,7 +301,7 @@ export default class HTMLExporter extends Exporter {
         if (hasAvatar) await this.saveAvatarIfNeeded(mxEv);
         // We have to wait for the component to be rendered before we can get the markup
         // so pass a deferred as a ref to the component.
-        const deferred = defer<void>();
+        const deferred = Promise.withResolvers<void>();
         const EventTile = this.getEventTile(mxEv, continuation, deferred.resolve);
         let eventTileMarkup: string;
 
diff --git a/src/vector/index.ts b/src/vector/index.ts
index af557c241b..f582a46c6b 100644
--- a/src/vector/index.ts
+++ b/src/vector/index.ts
@@ -49,6 +49,8 @@ function checkBrowserFeatures(): boolean {
     window.Modernizr.addTest("promiseprototypefinally", () => typeof window.Promise?.prototype?.finally === "function");
     // ES2020: http://262.ecma-international.org/#sec-promise.allsettled
     window.Modernizr.addTest("promiseallsettled", () => typeof window.Promise?.allSettled === "function");
+    // ES2024: https://2ality.com/2024/05/proposal-promise-with-resolvers.html
+    window.Modernizr.addTest("promisewithresolvers", () => typeof window.Promise?.withResolvers === "function");
     // ES2018: https://262.ecma-international.org/9.0/#sec-get-regexp.prototype.dotAll
     window.Modernizr.addTest(
         "regexpdotall",
diff --git a/src/vector/platform/IPCManager.ts b/src/vector/platform/IPCManager.ts
index eb0f411025..dc183f0cfb 100644
--- a/src/vector/platform/IPCManager.ts
+++ b/src/vector/platform/IPCManager.ts
@@ -5,7 +5,6 @@ SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Com
 Please see LICENSE files in the repository root for full details.
 */
 
-import { defer, type IDeferred } from "matrix-js-sdk/src/utils";
 import { logger } from "matrix-js-sdk/src/logger";
 
 import { type ElectronChannel } from "../../@types/global";
@@ -17,7 +16,7 @@ interface IPCPayload {
 }
 
 export class IPCManager {
-    private pendingIpcCalls: { [ipcCallId: number]: IDeferred<any> } = {};
+    private pendingIpcCalls: { [ipcCallId: number]: PromiseWithResolvers<any> } = {};
     private nextIpcCallId = 0;
 
     public constructor(
@@ -33,7 +32,7 @@ export class IPCManager {
     public async call(name: string, ...args: any[]): Promise<any> {
         // TODO this should be moved into the preload.js file.
         const ipcCallId = ++this.nextIpcCallId;
-        const deferred = defer<any>();
+        const deferred = Promise.withResolvers<any>();
         this.pendingIpcCalls[ipcCallId] = deferred;
         // Maybe add a timeout to these? Probably not necessary.
         window.electron!.send(this.sendChannel, { id: ipcCallId, name, args });
diff --git a/test/unit-tests/ContentMessages-test.ts b/test/unit-tests/ContentMessages-test.ts
index 2b08cd85e0..80b400568e 100644
--- a/test/unit-tests/ContentMessages-test.ts
+++ b/test/unit-tests/ContentMessages-test.ts
@@ -14,7 +14,6 @@ import {
     type UploadResponse,
 } from "matrix-js-sdk/src/matrix";
 import { type ImageInfo } from "matrix-js-sdk/src/types";
-import { defer } from "matrix-js-sdk/src/utils";
 import encrypt, { type IEncryptedFile } from "matrix-encrypt-attachment";
 
 import ContentMessages, { UploadCanceledError, uploadFile } from "../../src/ContentMessages";
@@ -338,7 +337,7 @@ describe("ContentMessages", () => {
 
     describe("cancelUpload", () => {
         it("should cancel in-flight upload", async () => {
-            const deferred = defer<UploadResponse>();
+            const deferred = Promise.withResolvers<UploadResponse>();
             mocked(client.uploadContent).mockReturnValue(deferred.promise);
             const file1 = new File([], "file1");
             const prom = contentMessages.sendContentToRoom(file1, roomId, undefined, client, undefined);
diff --git a/test/unit-tests/components/structures/MatrixChat-test.tsx b/test/unit-tests/components/structures/MatrixChat-test.tsx
index 8633b3cfcf..4e95f651b9 100644
--- a/test/unit-tests/components/structures/MatrixChat-test.tsx
+++ b/test/unit-tests/components/structures/MatrixChat-test.tsx
@@ -21,7 +21,7 @@ import { completeAuthorizationCodeGrant } from "matrix-js-sdk/src/oidc/authorize
 import { logger } from "matrix-js-sdk/src/logger";
 import { OidcError } from "matrix-js-sdk/src/oidc/error";
 import { type BearerTokenResponse } from "matrix-js-sdk/src/oidc/validate";
-import { defer, type IDeferred, sleep } from "matrix-js-sdk/src/utils";
+import { sleep } from "matrix-js-sdk/src/utils";
 import {
     CryptoEvent,
     type DeviceVerificationStatus,
@@ -85,7 +85,7 @@ describe("<MatrixChat />", () => {
     const deviceId = "qwertyui";
     const accessToken = "abc123";
     const refreshToken = "def456";
-    let bootstrapDeferred: IDeferred<void>;
+    let bootstrapDeferred: PromiseWithResolvers<void>;
     // reused in createClient mock below
     const getMockClientMethods = () => ({
         ...mockClientMethodsUser(userId),
@@ -248,7 +248,7 @@ describe("<MatrixChat />", () => {
             {} as ValidatedServerConfig,
         );
 
-        bootstrapDeferred = defer();
+        bootstrapDeferred = Promise.withResolvers();
 
         await clearAllModals();
     });
@@ -1513,7 +1513,7 @@ describe("<MatrixChat />", () => {
                 jest.spyOn(MatrixJs, "createClient").mockReturnValue(client);
 
                 // intercept initCrypto and have it block until we complete the deferred
-                const initCryptoCompleteDefer = defer();
+                const initCryptoCompleteDefer = Promise.withResolvers<void>();
                 const initCryptoCalled = new Promise<void>((resolve) => {
                     client.initRustCrypto.mockImplementation(() => {
                         resolve();
diff --git a/test/unit-tests/components/structures/RoomSearchView-test.tsx b/test/unit-tests/components/structures/RoomSearchView-test.tsx
index 300a4c1ab3..ab52e8012b 100644
--- a/test/unit-tests/components/structures/RoomSearchView-test.tsx
+++ b/test/unit-tests/components/structures/RoomSearchView-test.tsx
@@ -18,7 +18,6 @@ import {
     SearchResult,
     type ISearchResults,
 } from "matrix-js-sdk/src/matrix";
-import { defer } from "matrix-js-sdk/src/utils";
 
 import { RoomSearchView } from "../../../../src/components/structures/RoomSearchView";
 import ResizeNotifier from "../../../../src/utils/ResizeNotifier";
@@ -53,7 +52,7 @@ describe("<RoomSearchView/>", () => {
     });
 
     it("should show a spinner before the promise resolves", async () => {
-        const deferred = defer<ISearchResults>();
+        const deferred = Promise.withResolvers<ISearchResults>();
 
         render(
             <RoomSearchView
@@ -267,7 +266,7 @@ describe("<RoomSearchView/>", () => {
     });
 
     it("should handle resolutions after unmounting sanely", async () => {
-        const deferred = defer<ISearchResults>();
+        const deferred = Promise.withResolvers<ISearchResults>();
 
         const { unmount } = render(
             <MatrixClientContext.Provider value={client}>
@@ -291,7 +290,7 @@ describe("<RoomSearchView/>", () => {
     });
 
     it("should handle rejections after unmounting sanely", async () => {
-        const deferred = defer<ISearchResults>();
+        const deferred = Promise.withResolvers<ISearchResults>();
 
         const { unmount } = render(
             <MatrixClientContext.Provider value={client}>
@@ -316,7 +315,7 @@ describe("<RoomSearchView/>", () => {
 
     it("report error if one is encountered", async () => {
         const onUpdate = jest.fn();
-        const deferred = defer<ISearchResults>();
+        const deferred = Promise.withResolvers<ISearchResults>();
 
         render(
             <MatrixClientContext.Provider value={client}>
diff --git a/test/unit-tests/components/structures/RoomView-test.tsx b/test/unit-tests/components/structures/RoomView-test.tsx
index 1d6d3a8a9d..2d0d7f0d36 100644
--- a/test/unit-tests/components/structures/RoomView-test.tsx
+++ b/test/unit-tests/components/structures/RoomView-test.tsx
@@ -35,7 +35,6 @@ import {
     cleanup,
 } from "jest-matrix-react";
 import userEvent from "@testing-library/user-event";
-import { defer } from "matrix-js-sdk/src/utils";
 
 import {
     stubClient,
@@ -368,7 +367,7 @@ describe("RoomView", () => {
     it("should not display the timeline when the room encryption is loading", async () => {
         jest.spyOn(room, "getMyMembership").mockReturnValue(KnownMembership.Join);
         jest.spyOn(cli, "getCrypto").mockReturnValue(crypto);
-        const deferred = defer<boolean>();
+        const deferred = Promise.withResolvers<boolean>();
         jest.spyOn(cli.getCrypto()!, "isEncryptionEnabledInRoom").mockImplementation(() => deferred.promise);
 
         const { asFragment, container } = await mountRoomView();
diff --git a/test/unit-tests/components/views/elements/PowerSelector-test.tsx b/test/unit-tests/components/views/elements/PowerSelector-test.tsx
index ef35cf75a0..f98b6c7446 100644
--- a/test/unit-tests/components/views/elements/PowerSelector-test.tsx
+++ b/test/unit-tests/components/views/elements/PowerSelector-test.tsx
@@ -8,7 +8,6 @@ Please see LICENSE files in the repository root for full details.
 
 import React from "react";
 import { fireEvent, render, screen } from "jest-matrix-react";
-import { defer } from "matrix-js-sdk/src/utils";
 
 import PowerSelector from "../../../../../src/components/views/elements/PowerSelector";
 
@@ -70,7 +69,7 @@ describe("<PowerSelector />", () => {
     });
 
     it("should reset when onChange promise rejects", async () => {
-        const deferred = defer<void>();
+        const deferred = Promise.withResolvers<void>();
         render(
             <PowerSelector
                 value={25}
diff --git a/test/unit-tests/components/views/right_panel/UserInfo-test.tsx b/test/unit-tests/components/views/right_panel/UserInfo-test.tsx
index 71465fddbd..1a58b1e2e0 100644
--- a/test/unit-tests/components/views/right_panel/UserInfo-test.tsx
+++ b/test/unit-tests/components/views/right_panel/UserInfo-test.tsx
@@ -20,7 +20,6 @@ import {
     Device,
 } from "matrix-js-sdk/src/matrix";
 import { KnownMembership } from "matrix-js-sdk/src/types";
-import { defer } from "matrix-js-sdk/src/utils";
 import { EventEmitter } from "events";
 import {
     UserVerificationStatus,
@@ -714,7 +713,7 @@ describe("<UserOptionsSection />", () => {
     ])(
         "clicking »message« %s should start a DM",
         async (test: string, member: RoomMember | User, expectedAvatarUrl: string | undefined) => {
-            const deferred = defer<string>();
+            const deferred = Promise.withResolvers<string>();
             mocked(startDmOnFirstMessage).mockReturnValue(deferred.promise);
 
             renderComponent({ member });
diff --git a/test/unit-tests/components/views/settings/EventIndexPanel-test.tsx b/test/unit-tests/components/views/settings/EventIndexPanel-test.tsx
index 690d9ed2f3..738ff95c76 100644
--- a/test/unit-tests/components/views/settings/EventIndexPanel-test.tsx
+++ b/test/unit-tests/components/views/settings/EventIndexPanel-test.tsx
@@ -8,7 +8,6 @@ Please see LICENSE files in the repository root for full details.
 
 import React from "react";
 import { fireEvent, render, screen, within } from "jest-matrix-react";
-import { defer, type IDeferred } from "matrix-js-sdk/src/utils";
 
 import EventIndexPanel from "../../../../../src/components/views/settings/EventIndexPanel";
 import EventIndexPeg from "../../../../../src/indexing/EventIndexPeg";
@@ -140,9 +139,9 @@ describe("<EventIndexPanel />", () => {
         });
         it("enables event indexing on enable button click", async () => {
             jest.spyOn(EventIndexPeg, "supportIsInstalled").mockReturnValue(true);
-            let deferredInitEventIndex: IDeferred<boolean> | undefined;
+            let deferredInitEventIndex: PromiseWithResolvers<boolean> | undefined;
             jest.spyOn(EventIndexPeg, "initEventIndex").mockImplementation(() => {
-                deferredInitEventIndex = defer<boolean>();
+                deferredInitEventIndex = Promise.withResolvers<boolean>();
                 return deferredInitEventIndex.promise;
             });
 
diff --git a/test/unit-tests/components/views/settings/JoinRuleSettings-test.tsx b/test/unit-tests/components/views/settings/JoinRuleSettings-test.tsx
index 7fd34159a0..57e5dd39b3 100644
--- a/test/unit-tests/components/views/settings/JoinRuleSettings-test.tsx
+++ b/test/unit-tests/components/views/settings/JoinRuleSettings-test.tsx
@@ -21,7 +21,6 @@ import {
     Visibility,
 } from "matrix-js-sdk/src/matrix";
 import { KnownMembership } from "matrix-js-sdk/src/types";
-import { defer, type IDeferred } from "matrix-js-sdk/src/utils";
 
 import {
     clearAllModals,
@@ -162,7 +161,7 @@ describe("<JoinRuleSettings />", () => {
             });
 
             it(`upgrades room when changing join rule to ${joinRule}`, async () => {
-                const deferredInvites: IDeferred<any>[] = [];
+                const deferredInvites: PromiseWithResolvers<any>[] = [];
                 // room that doesn't support the join rule
                 const room = new Room(roomId, client, userId);
                 const parentSpace = new Room("!parentSpace:server.org", client, userId);
@@ -185,7 +184,7 @@ describe("<JoinRuleSettings />", () => {
                 // resolve invites by hand
                 // flushPromises is too blunt to test reliably
                 client.invite.mockImplementation(() => {
-                    const p = defer<{}>();
+                    const p = Promise.withResolvers<{}>();
                     deferredInvites.push(p);
                     return p.promise;
                 });
diff --git a/test/unit-tests/components/views/settings/encryption/DeleteKeyStoragePanel-test.tsx b/test/unit-tests/components/views/settings/encryption/DeleteKeyStoragePanel-test.tsx
index eb9e557025..8daca481ba 100644
--- a/test/unit-tests/components/views/settings/encryption/DeleteKeyStoragePanel-test.tsx
+++ b/test/unit-tests/components/views/settings/encryption/DeleteKeyStoragePanel-test.tsx
@@ -9,7 +9,6 @@ import React from "react";
 import { render, screen, waitFor } from "jest-matrix-react";
 import userEvent from "@testing-library/user-event";
 import { mocked } from "jest-mock";
-import { defer } from "matrix-js-sdk/src/utils";
 
 import type { MatrixClient } from "matrix-js-sdk/src/matrix";
 import { createTestClient, withClientContextRenderOptions } from "../../../../../test-utils";
@@ -72,7 +71,7 @@ describe("<DeleteKeyStoragePanel />", () => {
     });
 
     it("should wait with button disabled while setEnabled runs", async () => {
-        const setEnabledDefer = defer();
+        const setEnabledDefer = Promise.withResolvers<void>();
 
         mocked(useKeyStoragePanelViewModel).mockReturnValue({
             setEnabled: jest.fn().mockReturnValue(setEnabledDefer.promise),
diff --git a/test/unit-tests/components/views/settings/encryption/ResetIdentityPanel-test.tsx b/test/unit-tests/components/views/settings/encryption/ResetIdentityPanel-test.tsx
index 4dd538547c..0275b44142 100644
--- a/test/unit-tests/components/views/settings/encryption/ResetIdentityPanel-test.tsx
+++ b/test/unit-tests/components/views/settings/encryption/ResetIdentityPanel-test.tsx
@@ -7,7 +7,7 @@
 
 import React from "react";
 import { type MatrixClient } from "matrix-js-sdk/src/matrix";
-import { sleep, defer } from "matrix-js-sdk/src/utils";
+import { sleep } from "matrix-js-sdk/src/utils";
 import { render, screen } from "jest-matrix-react";
 import userEvent from "@testing-library/user-event";
 
@@ -33,7 +33,7 @@ describe("<ResetIdentityPanel />", () => {
 
         // We need to pause the reset so that we can check that it's providing
         // feedback to the user that something is happening.
-        const { promise: resetEncryptionPromise, resolve: resolveResetEncryption } = defer();
+        const { promise: resetEncryptionPromise, resolve: resolveResetEncryption } = Promise.withResolvers<void>();
         jest.spyOn(matrixClient.getCrypto()!, "resetEncryption").mockReturnValue(resetEncryptionPromise);
 
         const continueButton = screen.getByRole("button", { name: "Continue" });
diff --git a/test/unit-tests/components/views/settings/tabs/room/RolesRoomSettingsTab-test.tsx b/test/unit-tests/components/views/settings/tabs/room/RolesRoomSettingsTab-test.tsx
index 604fe8ae41..afd84ab33a 100644
--- a/test/unit-tests/components/views/settings/tabs/room/RolesRoomSettingsTab-test.tsx
+++ b/test/unit-tests/components/views/settings/tabs/room/RolesRoomSettingsTab-test.tsx
@@ -18,7 +18,6 @@ import {
 } from "matrix-js-sdk/src/matrix";
 import { KnownMembership } from "matrix-js-sdk/src/types";
 import { mocked } from "jest-mock";
-import { defer } from "matrix-js-sdk/src/utils";
 import userEvent from "@testing-library/user-event";
 
 import RolesRoomSettingsTab from "../../../../../../../src/components/views/settings/tabs/room/RolesRoomSettingsTab";
@@ -209,7 +208,7 @@ describe("RolesRoomSettingsTab", () => {
     });
 
     it("should roll back power level change on error", async () => {
-        const deferred = defer<ISendEventResponse>();
+        const deferred = Promise.withResolvers<ISendEventResponse>();
         mocked(cli.sendStateEvent).mockReturnValue(deferred.promise);
         mocked(cli.getRoom).mockReturnValue(room);
         // @ts-ignore - mocked doesn't support overloads properly
diff --git a/test/unit-tests/components/views/settings/tabs/user/AccountUserSettingsTab-test.tsx b/test/unit-tests/components/views/settings/tabs/user/AccountUserSettingsTab-test.tsx
index 531e66e00b..b12ba3a4ab 100644
--- a/test/unit-tests/components/views/settings/tabs/user/AccountUserSettingsTab-test.tsx
+++ b/test/unit-tests/components/views/settings/tabs/user/AccountUserSettingsTab-test.tsx
@@ -9,7 +9,6 @@ Please see LICENSE files in the repository root for full details.
 import { fireEvent, render, screen, within } from "jest-matrix-react";
 import React from "react";
 import { type MatrixClient, ThreepidMedium } from "matrix-js-sdk/src/matrix";
-import { defer } from "matrix-js-sdk/src/utils";
 import { logger } from "matrix-js-sdk/src/logger";
 import userEvent from "@testing-library/user-event";
 import { type MockedObject } from "jest-mock";
@@ -154,7 +153,7 @@ describe("<AccountUserSettingsTab />", () => {
                 (settingName) => settingName === UIFeature.Deactivate,
             );
 
-            const finishedDeferred = defer<[boolean]>();
+            const finishedDeferred = Promise.withResolvers<[boolean]>();
             const createDialogFn = jest.fn().mockReturnValue({ finished: finishedDeferred.promise });
             jest.spyOn(Modal, "createDialog").mockImplementation(createDialogFn);
 
@@ -169,7 +168,7 @@ describe("<AccountUserSettingsTab />", () => {
                 (settingName) => settingName === UIFeature.Deactivate,
             );
 
-            const finishedDeferred = defer<[boolean]>();
+            const finishedDeferred = Promise.withResolvers<[boolean]>();
             const createDialogFn = jest.fn().mockReturnValue({ finished: finishedDeferred.promise });
             jest.spyOn(Modal, "createDialog").mockImplementation(createDialogFn);
 
@@ -187,7 +186,7 @@ describe("<AccountUserSettingsTab />", () => {
                 (settingName) => settingName === UIFeature.Deactivate,
             );
 
-            const finishedDeferred = defer<[boolean]>();
+            const finishedDeferred = Promise.withResolvers<[boolean]>();
             const createDialogFn = jest.fn().mockReturnValue({ finished: finishedDeferred.promise });
             jest.spyOn(Modal, "createDialog").mockImplementation(createDialogFn);
 
diff --git a/test/unit-tests/components/views/settings/tabs/user/SessionManagerTab-test.tsx b/test/unit-tests/components/views/settings/tabs/user/SessionManagerTab-test.tsx
index 2dcc6d1cd6..709d4e1714 100644
--- a/test/unit-tests/components/views/settings/tabs/user/SessionManagerTab-test.tsx
+++ b/test/unit-tests/components/views/settings/tabs/user/SessionManagerTab-test.tsx
@@ -19,7 +19,7 @@ import {
 } from "jest-matrix-react";
 import { logger } from "matrix-js-sdk/src/logger";
 import { type CryptoApi, DeviceVerificationStatus, type VerificationRequest } from "matrix-js-sdk/src/crypto-api";
-import { defer, sleep } from "matrix-js-sdk/src/utils";
+import { sleep } from "matrix-js-sdk/src/utils";
 import {
     ClientEvent,
     Device,
@@ -899,7 +899,7 @@ describe("<SessionManagerTab />", () => {
             });
 
             it("deletes a device when interactive auth is not required", async () => {
-                const deferredDeleteMultipleDevices = defer<{}>();
+                const deferredDeleteMultipleDevices = Promise.withResolvers<{}>();
                 mockClient.deleteMultipleDevices.mockReturnValue(deferredDeleteMultipleDevices.promise);
                 mockClient.getDevices.mockResolvedValue({
                     devices: [alicesDevice, alicesMobileDevice, alicesOlderMobileDevice],
@@ -1108,7 +1108,7 @@ describe("<SessionManagerTab />", () => {
                 // get a handle for resolving the delete call
                 // because promise flushing after the confirm modal is resolving this too
                 // and we want to test the loading state here
-                const resolveDeleteRequest = defer<IAuthData>();
+                const resolveDeleteRequest = Promise.withResolvers<IAuthData>();
                 mockClient.deleteMultipleDevices.mockImplementation(async () => {
                     await resolveDeleteRequest.promise;
                     return {};
diff --git a/test/unit-tests/dispatcher/dispatcher-test.ts b/test/unit-tests/dispatcher/dispatcher-test.ts
index 711fad2b5e..4b8fc31d28 100644
--- a/test/unit-tests/dispatcher/dispatcher-test.ts
+++ b/test/unit-tests/dispatcher/dispatcher-test.ts
@@ -6,8 +6,6 @@ SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Com
 Please see LICENSE files in the repository root for full details.
 */
 
-import { defer } from "matrix-js-sdk/src/utils";
-
 import defaultDispatcher from "../../../src/dispatcher/dispatcher";
 import { Action } from "../../../src/dispatcher/actions";
 import { AsyncActionPayload } from "../../../src/dispatcher/payloads";
@@ -20,8 +18,8 @@ describe("MatrixDispatcher", () => {
     });
 
     it("should execute callbacks in registered order", async () => {
-        const deferred1 = defer<number>();
-        const deferred2 = defer<number>();
+        const deferred1 = Promise.withResolvers<number>();
+        const deferred2 = Promise.withResolvers<number>();
 
         const fn1 = jest.fn(() => deferred1.resolve(1));
         const fn2 = jest.fn(() => deferred2.resolve(2));
@@ -36,8 +34,8 @@ describe("MatrixDispatcher", () => {
     });
 
     it("should skip the queue for the given callback", async () => {
-        const deferred1 = defer<number>();
-        const deferred2 = defer<number>();
+        const deferred1 = Promise.withResolvers<number>();
+        const deferred2 = Promise.withResolvers<number>();
 
         const fn1 = jest.fn(() => deferred1.resolve(1));
         const fn2 = jest.fn(() => deferred2.resolve(2));
diff --git a/test/unit-tests/settings/controllers/ServerSupportUnstableFeatureController-test.ts b/test/unit-tests/settings/controllers/ServerSupportUnstableFeatureController-test.ts
index fe96ca448b..cab82f8d32 100644
--- a/test/unit-tests/settings/controllers/ServerSupportUnstableFeatureController-test.ts
+++ b/test/unit-tests/settings/controllers/ServerSupportUnstableFeatureController-test.ts
@@ -6,7 +6,6 @@ SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Com
 Please see LICENSE files in the repository root for full details.
 */
 
-import { defer } from "matrix-js-sdk/src/utils";
 import { type MatrixClient } from "matrix-js-sdk/src/matrix";
 
 import ServerSupportUnstableFeatureController from "../../../../src/settings/controllers/ServerSupportUnstableFeatureController";
@@ -34,7 +33,7 @@ describe("ServerSupportUnstableFeatureController", () => {
             controller,
         };
 
-        const deferred = defer<any>();
+        const deferred = Promise.withResolvers<any>();
         watchers.watchSetting(setting, null, deferred.resolve);
         MatrixClientBackedController.matrixClient = cli;
         await deferred.promise;
diff --git a/test/unit-tests/stores/SpaceStore-test.ts b/test/unit-tests/stores/SpaceStore-test.ts
index 7471ae118b..6b6b6c1bc1 100644
--- a/test/unit-tests/stores/SpaceStore-test.ts
+++ b/test/unit-tests/stores/SpaceStore-test.ts
@@ -20,7 +20,6 @@ import {
     type RoomState,
 } from "matrix-js-sdk/src/matrix";
 import { KnownMembership } from "matrix-js-sdk/src/types";
-import { defer } from "matrix-js-sdk/src/utils";
 
 import SpaceStore from "../../../src/stores/spaces/SpaceStore";
 import {
@@ -1010,7 +1009,7 @@ describe("SpaceStore", () => {
 
         await run();
 
-        const deferred = defer<boolean>();
+        const deferred = Promise.withResolvers<boolean>();
         space.loadMembersIfNeeded.mockImplementation(() => {
             const event = mkEvent({
                 event: true,
diff --git a/tsconfig.json b/tsconfig.json
index 854af09239..10d7c216b6 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -14,7 +14,7 @@
         "outDir": "./lib",
         "declaration": true,
         "jsx": "react",
-        "lib": ["es2022", "dom", "dom.iterable"],
+        "lib": ["es2022", "es2024.promise", "dom", "dom.iterable"],
         "strict": true,
         "paths": {
             "jest-matrix-react": ["./test/test-utils/jest-matrix-react"]