diff --git a/res/css/_common.scss b/res/css/_common.scss
index e062e0bd73..a4ef603242 100644
--- a/res/css/_common.scss
+++ b/res/css/_common.scss
@@ -42,10 +42,15 @@ pre, code {
     font-size: 100% !important;
 }
 
-.error, .warning {
+.error, .warning,
+.text-error, .text-warning {
     color: $warning-color;
 }
 
+.text-success {
+    color: $accent-color;
+}
+
 b {
     // On Firefox, the default weight for `<b>` is `bolder` which results in no bold
     // effect since we only have specific weights of our fonts available.
diff --git a/src/components/views/settings/tabs/user/GeneralUserSettingsTab.js b/src/components/views/settings/tabs/user/GeneralUserSettingsTab.js
index 304bb6449f..e9b30430a3 100644
--- a/src/components/views/settings/tabs/user/GeneralUserSettingsTab.js
+++ b/src/components/views/settings/tabs/user/GeneralUserSettingsTab.js
@@ -61,6 +61,8 @@ export default class GeneralUserSettingsTab extends React.Component {
             emails: [],
             msisdns: [],
             ...this._calculateThemeState(),
+            customThemeUrl: "",
+            customThemeMessage: {isError: false, text: ""},
         };
 
         this.dispatcherRef = dis.register(this._onAction);
@@ -274,6 +276,41 @@ export default class GeneralUserSettingsTab extends React.Component {
         });
     };
 
+    _onAddCustomTheme = async () => {
+        let currentThemes = SettingsStore.getValue("custom_themes");
+        if (!currentThemes) currentThemes = [];
+        currentThemes = currentThemes.map(c => c); // cheap clone
+
+        if (this._themeTimer) {
+            clearTimeout(this._themeTimer);
+        }
+
+        try {
+            const r = await fetch(this.state.customThemeUrl);
+            const themeInfo = await r.json();
+            if (!themeInfo || typeof(themeInfo['name']) !== 'string' || typeof(themeInfo['colors']) !== 'object') {
+                this.setState({customThemeMessage: {text: _t("Invalid theme schema."), isError: true}});
+                return;
+            }
+            currentThemes.push(themeInfo);
+        } catch (e) {
+            console.error(e);
+            this.setState({customThemeMessage: {text: _t("Error downloading theme information."), isError: true}});
+            return; // Don't continue on error
+        }
+
+        await SettingsStore.setValue("custom_themes", null, SettingLevel.ACCOUNT, currentThemes);
+        this.setState({customThemeUrl: "", customThemeMessage: {text: _t("Theme added!"), isError: false}});
+
+        this._themeTimer = setTimeout(() => {
+            this.setState({customThemeMessage: {text: "", isError: false}});
+        }, 3000);
+    };
+
+    _onCustomThemeChange = (e) => {
+        this.setState({customThemeUrl: e.target.value});
+    };
+
     _renderProfileSection() {
         return (
             <div className="mx_SettingsTab_section">
@@ -368,6 +405,45 @@ export default class GeneralUserSettingsTab extends React.Component {
                 />
             </div>;
         }
+
+        let customThemeForm;
+        if (SettingsStore.isFeatureEnabled("feature_custom_themes")) {
+            let messageElement = null;
+            if (this.state.customThemeMessage.text) {
+                if (this.state.customThemeMessage.isError) {
+                    messageElement = <div className='text-error'>{this.state.customThemeMessage.text}</div>;
+                } else {
+                    messageElement = <div className='text-success'>{this.state.customThemeMessage.text}</div>;
+                }
+            }
+            customThemeForm = (
+                <div className='mx_SettingsTab_section'>
+                    <form onSubmit={this._onAddCustomTheme}>
+                        <Field
+                            label={_t("Custom theme URL")}
+                            type='text'
+                            id='mx_GeneralUserSettingsTab_customThemeInput'
+                            autoComplete="off"
+                            onChange={this._onCustomThemeChange}
+                            value={this.state.customThemeUrl}
+                        />
+                        <AccessibleButton
+                            onClick={this._onAddCustomTheme}
+                            type="submit" kind="primary_sm"
+                            disabled={!this.state.customThemeUrl.trim()}
+                        >{_t("Add theme")}</AccessibleButton>
+                        {messageElement}
+                    </form>
+                </div>
+            );
+        }
+
+        const themes = Object.entries(enumerateThemes())
+            .map(p => ({id: p[0], name: p[1]})); // convert pairs to objects for code readability
+        const builtInThemes = themes.filter(p => !p.id.startsWith("custom-"));
+        const customThemes = themes.filter(p => !builtInThemes.includes(p))
+            .sort((a, b) => a.name.localeCompare(b.name));
+        const orderedThemes = [...builtInThemes, ...customThemes];
         return (
             <div className="mx_SettingsTab_section mx_GeneralUserSettingsTab_themeSection">
                 <span className="mx_SettingsTab_subheading">{_t("Theme")}</span>
@@ -376,10 +452,11 @@ export default class GeneralUserSettingsTab extends React.Component {
                        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>;
+                    {orderedThemes.map(theme => {
+                        return <option key={theme.id} value={theme.id}>{theme.name}</option>;
                     })}
                 </Field>
+                {customThemeForm}
                 <SettingsFlag name="useCompactLayout" level={SettingLevel.ACCOUNT} />
             </div>
         );
diff --git a/src/i18n/strings/en_EN.json b/src/i18n/strings/en_EN.json
index d92cf41f5b..42120588c3 100644
--- a/src/i18n/strings/en_EN.json
+++ b/src/i18n/strings/en_EN.json
@@ -385,6 +385,7 @@
     "Multiple integration managers": "Multiple integration managers",
     "Try out new ways to ignore people (experimental)": "Try out new ways to ignore people (experimental)",
     "Show a presence dot next to DMs in the room list": "Show a presence dot next to DMs in the room list",
+    "Support adding custom themes": "Support adding custom themes",
     "Enable cross-signing to verify per-user instead of per-session (in development)": "Enable cross-signing to verify per-user instead of per-session (in development)",
     "Enable local event indexing and E2EE search (requires restart)": "Enable local event indexing and E2EE search (requires restart)",
     "Show info about bridges in room settings": "Show info about bridges in room settings",
@@ -708,12 +709,17 @@
     "Failed to change password. Is your password correct?": "Failed to change password. Is your password correct?",
     "Success": "Success",
     "Your password was successfully changed. You will not receive push notifications on other sessions until you log back in to them": "Your password was successfully changed. You will not receive push notifications on other sessions until you log back in to them",
+    "Invalid theme schema.": "Invalid theme schema.",
+    "Error downloading theme information.": "Error downloading theme information.",
+    "Theme added!": "Theme added!",
     "Profile": "Profile",
     "Email addresses": "Email addresses",
     "Phone numbers": "Phone numbers",
     "Set a new account password...": "Set a new account password...",
     "Account": "Account",
     "Language and region": "Language and region",
+    "Custom theme URL": "Custom theme URL",
+    "Add theme": "Add theme",
     "Theme": "Theme",
     "Agree to the identity server (%(serverName)s) Terms of Service to allow yourself to be discoverable by email address or phone number.": "Agree to the identity server (%(serverName)s) Terms of Service to allow yourself to be discoverable by email address or phone number.",
     "Account management": "Account management",
diff --git a/src/settings/Settings.js b/src/settings/Settings.js
index b77fb392e9..ba6df47a04 100644
--- a/src/settings/Settings.js
+++ b/src/settings/Settings.js
@@ -134,6 +134,12 @@ export const SETTINGS = {
         supportedLevels: LEVELS_FEATURE,
         default: false,
     },
+    "feature_custom_themes": {
+        isFeature: true,
+        displayName: _td("Support adding custom themes"),
+        supportedLevels: LEVELS_FEATURE,
+        default: false,
+    },
     "mjolnirRooms": {
         supportedLevels: ['account'],
         default: [],