diff --git a/src/components/structures/MatrixChat.js b/src/components/structures/MatrixChat.js
index c6efb56a9d..661a0c7077 100644
--- a/src/components/structures/MatrixChat.js
+++ b/src/components/structures/MatrixChat.js
@@ -59,7 +59,7 @@ import { ValidatedServerConfig } from "../../utils/AutoDiscoveryUtils";
 import AutoDiscoveryUtils from "../../utils/AutoDiscoveryUtils";
 import DMRoomMap from '../../utils/DMRoomMap';
 import { countRoomsWithNotif } from '../../RoomNotifs';
-import { setTheme } from "../../theme";
+import { ThemeWatcher } from "../../theme";
 import { storeRoomAliasInCache } from '../../RoomAliasCache';
 import { defer } from "../../utils/promise";
 
@@ -274,7 +274,8 @@ export default createReactClass({
 
     componentDidMount: function() {
         this.dispatcherRef = dis.register(this.onAction);
-        this._themeWatchRef = SettingsStore.watchSetting("theme", null, this._onThemeChanged);
+        this._themeWatcher = new ThemeWatcher();
+        this._themeWatcher.start();
 
         this.focusComposer = false;
 
@@ -361,7 +362,7 @@ export default createReactClass({
     componentWillUnmount: function() {
         Lifecycle.stopMatrixClient();
         dis.unregister(this.dispatcherRef);
-        SettingsStore.unwatchSetting(this._themeWatchRef);
+        this._themeWatcher.stop();
         window.removeEventListener("focus", this.onFocus);
         window.removeEventListener('resize', this.handleResize);
         this.state.resizeNotifier.removeListener("middlePanelResized", this._dispatchTimelineResize);
@@ -384,13 +385,6 @@ export default createReactClass({
         }
     },
 
-    _onThemeChanged: function(settingName, roomId, atLevel, newValue) {
-        dis.dispatch({
-            action: 'set_theme',
-            value: newValue,
-        });
-    },
-
     startPageChangeTimer() {
         // Tor doesn't support performance
         if (!performance || !performance.mark) return null;
@@ -672,9 +666,6 @@ export default createReactClass({
                 });
                 break;
             }
-            case 'set_theme':
-                setTheme(payload.value);
-                break;
             case 'on_logging_in':
                 // We are now logging in, so set the state to reflect that
                 // NB. This does not touch 'ready' since if our dispatches
diff --git a/src/components/views/settings/tabs/user/GeneralUserSettingsTab.js b/src/components/views/settings/tabs/user/GeneralUserSettingsTab.js
index d400e7a839..b518f7c81b 100644
--- a/src/components/views/settings/tabs/user/GeneralUserSettingsTab.js
+++ b/src/components/views/settings/tabs/user/GeneralUserSettingsTab.js
@@ -27,7 +27,7 @@ import LanguageDropdown from "../../../elements/LanguageDropdown";
 import AccessibleButton from "../../../elements/AccessibleButton";
 import DeactivateAccountDialog from "../../../dialogs/DeactivateAccountDialog";
 import PropTypes from "prop-types";
-import {enumerateThemes} from "../../../../../theme";
+import {enumerateThemes, ThemeWatcher} from "../../../../../theme";
 import PlatformPeg from "../../../../../PlatformPeg";
 import MatrixClientPeg from "../../../../../MatrixClientPeg";
 import sdk from "../../../../..";
@@ -50,6 +50,7 @@ export default class GeneralUserSettingsTab extends React.Component {
         this.state = {
             language: languageHandler.getCurrentLanguage(),
             theme: SettingsStore.getValueAt(SettingLevel.ACCOUNT, "theme"),
+            useSystemTheme: SettingsStore.getValueAt(SettingLevel.DEVICE, "use_system_theme"),
             haveIdServer: Boolean(MatrixClientPeg.get().getIdentityServerUrl()),
             serverSupportsSeparateAddAndBind: null,
             idServerHasUnsignedTerms: false,
@@ -177,16 +178,25 @@ export default class GeneralUserSettingsTab extends React.Component {
         // so remember what the value was before we tried to set it so we can revert
         const oldTheme = SettingsStore.getValue('theme');
         SettingsStore.setValue("theme", null, SettingLevel.ACCOUNT, newTheme).catch(() => {
-            dis.dispatch({action: 'set_theme', value: oldTheme});
+            dis.dispatch({action: 'recheck_theme'});
             this.setState({theme: oldTheme});
         });
         this.setState({theme: newTheme});
         // The settings watcher doesn't fire until the echo comes back from the
         // server, so to make the theme change immediately we need to manually
         // do the dispatch now
-        dis.dispatch({action: 'set_theme', value: newTheme});
+        // XXX: The local echoed value appears to be unreliable, in particular
+        // when settings custom themes(!) so adding forceTheme to override
+        // the value from settings.
+        dis.dispatch({action: 'recheck_theme', forceTheme: newTheme});
     };
 
+    _onUseSystemThemeChanged = (checked) => {
+        this.setState({useSystemTheme: checked});
+        dis.dispatch({action: 'recheck_theme'});
+    }
+
+
     _onPasswordChangeError = (err) => {
         // TODO: Figure out a design that doesn't involve replacing the current dialog
         let errMsg = err.error || "";
@@ -297,11 +307,24 @@ export default class GeneralUserSettingsTab extends React.Component {
 
     _renderThemeSection() {
         const SettingsFlag = sdk.getComponent("views.elements.SettingsFlag");
+
+        const themeWatcher = new ThemeWatcher();
+        let systemThemeSection;
+        if (themeWatcher.isSystemThemeSupported()) {
+            systemThemeSection = <div>
+                <SettingsFlag name="use_system_theme" level={SettingLevel.DEVICE}
+                    onChange={this._onUseSystemThemeChanged}
+                />
+            </div>;
+        }
         return (
             <div className="mx_SettingsTab_section mx_GeneralUserSettingsTab_themeSection">
                 <span className="mx_SettingsTab_subheading">{_t("Theme")}</span>
+                {systemThemeSection}
                 <Field id="theme" label={_t("Theme")} element="select"
-                       value={this.state.theme} onChange={this._onThemeChange}>
+                       value={this.state.theme} onChange={this._onThemeChange}
+                       disabled={this.state.useSystemTheme}
+                >
                     {Object.entries(enumerateThemes()).map(([theme, text]) => {
                         return <option key={theme} value={theme}>{text}</option>;
                     })}
diff --git a/src/i18n/strings/en_EN.json b/src/i18n/strings/en_EN.json
index a4781fc52e..7709a4a398 100644
--- a/src/i18n/strings/en_EN.json
+++ b/src/i18n/strings/en_EN.json
@@ -364,6 +364,7 @@
     "Automatically replace plain text Emoji": "Automatically replace plain text Emoji",
     "Mirror local video feed": "Mirror local video feed",
     "Enable Community Filter Panel": "Enable Community Filter Panel",
+    "Match system dark mode setting": "Match system dark mode setting",
     "Allow Peer-to-Peer for 1:1 calls": "Allow Peer-to-Peer for 1:1 calls",
     "Send analytics data": "Send analytics data",
     "Never send encrypted messages to unverified devices from this device": "Never send encrypted messages to unverified devices from this device",
diff --git a/src/settings/Settings.js b/src/settings/Settings.js
index 92f7da7dae..89693f7c50 100644
--- a/src/settings/Settings.js
+++ b/src/settings/Settings.js
@@ -281,6 +281,11 @@ export const SETTINGS = {
         supportedLevels: LEVELS_ACCOUNT_SETTINGS,
         default: [],
     },
+    "use_system_theme": {
+        supportedLevels: LEVELS_DEVICE_ONLY_SETTINGS,
+        default: true,
+        displayName: _td("Match system dark mode setting"),
+    },
     "webRtcAllowPeerToPeer": {
         supportedLevels: LEVELS_DEVICE_ONLY_SETTINGS_WITH_CONFIG,
         displayName: _td('Allow Peer-to-Peer for 1:1 calls'),
diff --git a/src/theme.js b/src/theme.js
index 8a15c606d7..fa7e3f783b 100644
--- a/src/theme.js
+++ b/src/theme.js
@@ -19,8 +19,75 @@ import {_t} from "./languageHandler";
 
 export const DEFAULT_THEME = "light";
 import Tinter from "./Tinter";
+import dis from "./dispatcher";
 import SettingsStore from "./settings/SettingsStore";
 
+export class ThemeWatcher {
+    static _instance = null;
+
+    constructor() {
+        this._themeWatchRef = null;
+        this._systemThemeWatchRef = null;
+        this._dispatcherRef = null;
+
+        // we have both here as each may either match or not match, so by having both
+        // we can get the tristate of dark/light/unsupported
+        this._preferDark = global.matchMedia("(prefers-color-scheme: dark)");
+        this._preferLight = global.matchMedia("(prefers-color-scheme: light)");
+
+        this._currentTheme = this.getEffectiveTheme();
+    }
+
+    start() {
+        this._themeWatchRef = SettingsStore.watchSetting("theme", null, this._onChange);
+        this._systemThemeWatchRef = SettingsStore.watchSetting("use_system_theme", null, this._onChange);
+        this._preferDark.addEventListener('change', this._onChange);
+        this._preferLight.addEventListener('change', this._onChange);
+        this._dispatcherRef = dis.register(this._onAction);
+    }
+
+    stop() {
+        this._preferDark.removeEventListener('change', this._onChange);
+        this._preferLight.removeEventListener('change', this._onChange);
+        SettingsStore.unwatchSetting(this._systemThemeWatchRef);
+        SettingsStore.unwatchSetting(this._themeWatchRef);
+        dis.unregister(this._dispatcherRef);
+    }
+
+    _onChange = () => {
+        this.recheck();
+    }
+
+    _onAction = (payload) => {
+        if (payload.action === 'recheck_theme') {
+            // XXX forceTheme
+            this.recheck(payload.forceTheme);
+        }
+    }
+
+    // XXX: forceTheme param aded here as local echo appears to be unreliable
+    // https://github.com/vector-im/riot-web/issues/11443
+    recheck(forceTheme) {
+        const oldTheme = this._currentTheme;
+        this._currentTheme = forceTheme === undefined ? this.getEffectiveTheme() : forceTheme;
+        if (oldTheme !== this._currentTheme) {
+            setTheme(this._currentTheme);
+        }
+    }
+
+    getEffectiveTheme() {
+        if (SettingsStore.getValue('use_system_theme')) {
+            if (this._preferDark.matches) return 'dark';
+            if (this._preferLight.matches) return 'light';
+        }
+        return SettingsStore.getValue('theme');
+    }
+
+    isSystemThemeSupported() {
+        return this._preferDark.matches || this._preferLight.matches;
+    }
+}
+
 export function enumerateThemes() {
     const BUILTIN_THEMES = {
         "light": _t("Light theme"),
@@ -83,7 +150,8 @@ export function getBaseTheme(theme) {
  */
 export function setTheme(theme) {
     if (!theme) {
-        theme = SettingsStore.getValue("theme");
+        const themeWatcher = new ThemeWatcher();
+        theme = themeWatcher.getEffectiveTheme();
     }
     let stylesheetName = theme;
     if (theme.startsWith("custom-")) {