diff --git a/CHANGELOG.md b/CHANGELOG.md
index b68de467d7f19..e2d7c89444bc7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@
 - [vscode] added support for `autoClosingPairs` in the `LanguageConfiguration ` VS Code API [#13088](https://github.com/eclipse-theia/theia/pull/13088) - contributed on behalf of STMicroelectronics
 - [task] prevent task widget title from being changed by task process [#13003](https://github.com/eclipse-theia/theia/pull/13003)
 - [vscode] added Notebook CodeActionKind [#13093](https://github.com/eclipse-theia/theia/pull/13093) - contributed on behalf of STMicroelectronics
+- [vscode] added support for editor.indentSize API [#13105](https://github.com/eclipse-theia/theia/pull/13105) - contributed on behalf of STMicroelectronics
 - [vscode] added support to env.ondidChangeShell event [#13097](https://github.com/eclipse-theia/theia/pull/13097) - contributed on behalf of STMicroelectronics
 - [task] support `isDefault: false` in task group definition [#13075](https://github.com/eclipse-theia/theia/pull/13075) - contributed on behalf of STMicroelectronics
 
diff --git a/packages/monaco/src/browser/monaco-command.ts b/packages/monaco/src/browser/monaco-command.ts
index 8d22defd108f7..323f4408a655f 100644
--- a/packages/monaco/src/browser/monaco-command.ts
+++ b/packages/monaco/src/browser/monaco-command.ts
@@ -265,10 +265,12 @@ export class MonacoEditorCommandHandlers implements CommandContribution {
             ({
                 label: size === tabSize ? size + '   ' + nls.localizeByDefault('Configured Tab Size') : size.toString(),
                 // eslint-disable-next-line @typescript-eslint/no-explicit-any
-                execute: () => model.updateOptions({
-                    tabSize: size || tabSize,
-                    insertSpaces: useSpaces
-                })
+                execute: () =>
+                    model.updateOptions({
+                        tabSize: size || tabSize,
+                        indentSize: size || tabSize,
+                        insertSpaces: useSpaces
+                    })
             })
             );
             this.quickInputService?.showQuickPick(tabSizeOptions, { placeholder: nls.localizeByDefault('Select Tab Size for Current File') });
diff --git a/packages/monaco/src/browser/monaco-status-bar-contribution.ts b/packages/monaco/src/browser/monaco-status-bar-contribution.ts
index 4a7ba08752c5a..fae85805e9f1a 100644
--- a/packages/monaco/src/browser/monaco-status-bar-contribution.ts
+++ b/packages/monaco/src/browser/monaco-status-bar-contribution.ts
@@ -67,8 +67,9 @@ export class MonacoStatusBarContribution implements FrontendApplicationContribut
         if (editor && editorModel) {
             const modelOptions = editorModel.getOptions();
             const tabSize = modelOptions.tabSize;
+            const indentSize = modelOptions.indentSize;
             const spaceOrTabSizeMessage = modelOptions.insertSpaces
-                ? nls.localizeByDefault('Spaces: {0}', tabSize)
+                ? nls.localizeByDefault('Spaces: {0}', indentSize)
                 : nls.localizeByDefault('Tab Size: {0}', tabSize);
             this.statusBar.setElement('editor-status-tabbing-config', {
                 text: spaceOrTabSizeMessage,
diff --git a/packages/monaco/src/browser/monaco-text-model-service.ts b/packages/monaco/src/browser/monaco-text-model-service.ts
index 8c7bd41749762..d4440b4d80946 100644
--- a/packages/monaco/src/browser/monaco-text-model-service.ts
+++ b/packages/monaco/src/browser/monaco-text-model-service.ts
@@ -127,12 +127,15 @@ export class MonacoTextModelService implements ITextModelService {
 
     protected readonly modelOptions: { [name: string]: (keyof ITextModelUpdateOptions | undefined) } = {
         'editor.tabSize': 'tabSize',
-        'editor.insertSpaces': 'insertSpaces'
+        'editor.insertSpaces': 'insertSpaces',
+        'editor.indentSize': 'indentSize'
     };
 
     protected toModelOption(editorPreference: EditorPreferenceChange['preferenceName']): keyof ITextModelUpdateOptions | undefined {
         switch (editorPreference) {
             case 'editor.tabSize': return 'tabSize';
+            // @monaco-uplift: uncomment this line once 'editor.indentSize' preference is available
+            //  case 'editor.indentSize': return 'indentSize';
             case 'editor.insertSpaces': return 'insertSpaces';
             case 'editor.bracketPairColorization.enabled':
             case 'editor.bracketPairColorization.independentColorPoolPerBracketType':
@@ -170,6 +173,8 @@ export class MonacoTextModelService implements ITextModelService {
         const overrideIdentifier = typeof arg === 'string' ? undefined : arg.languageId;
         return {
             tabSize: this.editorPreferences.get({ preferenceName: 'editor.tabSize', overrideIdentifier }, undefined, uri),
+            // @monaco-uplift: when available, switch to 'editor.indentSize' preference.
+            indentSize: this.editorPreferences.get({ preferenceName: 'editor.tabSize', overrideIdentifier }, undefined, uri),
             insertSpaces: this.editorPreferences.get({ preferenceName: 'editor.insertSpaces', overrideIdentifier }, undefined, uri),
             bracketColorizationOptions: {
                 enabled: this.editorPreferences.get({ preferenceName: 'editor.bracketPairColorization.enabled', overrideIdentifier }, undefined, uri),
diff --git a/packages/plugin-ext/src/common/plugin-api-rpc.ts b/packages/plugin-ext/src/common/plugin-api-rpc.ts
index 6d56cd92712f6..71b67d64b82a7 100644
--- a/packages/plugin-ext/src/common/plugin-api-rpc.ts
+++ b/packages/plugin-ext/src/common/plugin-api-rpc.ts
@@ -1125,6 +1125,7 @@ export interface Selection {
 
 export interface TextEditorConfiguration {
     tabSize: number;
+    indentSize: number;
     insertSpaces: boolean;
     cursorStyle: TextEditorCursorStyle;
     lineNumbers: TextEditorLineNumbersStyle;
@@ -1132,6 +1133,7 @@ export interface TextEditorConfiguration {
 
 export interface TextEditorConfigurationUpdate {
     tabSize?: number | 'auto';
+    indentSize?: number | 'tabSize';
     insertSpaces?: boolean | 'auto';
     cursorStyle?: TextEditorCursorStyle;
     lineNumbers?: TextEditorLineNumbersStyle;
diff --git a/packages/plugin-ext/src/main/browser/text-editor-main.ts b/packages/plugin-ext/src/main/browser/text-editor-main.ts
index 1dea02aa16b8f..17656f9a85d2e 100644
--- a/packages/plugin-ext/src/main/browser/text-editor-main.ts
+++ b/packages/plugin-ext/src/main/browser/text-editor-main.ts
@@ -194,6 +194,13 @@ export class TextEditorMain implements Disposable {
         if (typeof newConfiguration.tabSize !== 'undefined') {
             newOpts.tabSize = newConfiguration.tabSize;
         }
+        if (typeof newConfiguration.indentSize !== 'undefined') {
+            if (newConfiguration.indentSize === 'tabSize') {
+                newOpts.indentSize = newConfiguration.tabSize;
+            } else if (typeof newConfiguration.indentSize == 'number') {
+                newOpts.indentSize = newConfiguration.indentSize;
+            }
+        }
         this.model.updateOptions(newOpts);
     }
 
@@ -408,6 +415,7 @@ export class TextEditorPropertiesMain {
         const modelOptions = model.getOptions();
         return {
             insertSpaces: modelOptions.insertSpaces,
+            indentSize: modelOptions.indentSize,
             tabSize: modelOptions.tabSize,
             cursorStyle,
             lineNumbers,
@@ -443,6 +451,7 @@ export class TextEditorPropertiesMain {
         return (
             a.tabSize === b.tabSize
             && a.insertSpaces === b.insertSpaces
+            && a.indentSize === b.indentSize
             && a.cursorStyle === b.cursorStyle
             && a.lineNumbers === b.lineNumbers
         );
diff --git a/packages/plugin-ext/src/plugin/text-editor.ts b/packages/plugin-ext/src/plugin/text-editor.ts
index 02852b04cf469..85b87747107ba 100644
--- a/packages/plugin-ext/src/plugin/text-editor.ts
+++ b/packages/plugin-ext/src/plugin/text-editor.ts
@@ -277,7 +277,8 @@ export class TextEditorExt implements theia.TextEditor {
 }
 
 export class TextEditorOptionsExt implements theia.TextEditorOptions {
-    private _tabSize?: number;
+    private _tabSize: number;
+    private _indentSize: number | 'tabSize';
     private _insertSpace: boolean;
     private _cursorStyle: TextEditorCursorStyle;
     private _lineNumbers: TextEditorLineNumbersStyle;
@@ -289,12 +290,13 @@ export class TextEditorOptionsExt implements theia.TextEditorOptions {
 
     accept(source: TextEditorConfiguration): void {
         this._tabSize = source.tabSize;
+        this._indentSize = source.indentSize;
         this._insertSpace = source.insertSpaces;
         this._cursorStyle = source.cursorStyle;
         this._lineNumbers = source.lineNumbers;
     }
 
-    get tabSize(): number | string | undefined {
+    get tabSize(): number {
         return this._tabSize;
     }
 
@@ -305,10 +307,10 @@ export class TextEditorOptionsExt implements theia.TextEditorOptions {
         }
 
         if (typeof tabSize === 'number') {
-            if (this.tabSize === tabSize) {
+            if (this._tabSize === tabSize) {
                 return;
             }
-            this.tabSize = tabSize;
+            this._tabSize = tabSize;
         }
         warnOnError(this.proxy.$trySetOptions(this.id, {
             tabSize
@@ -334,6 +336,51 @@ export class TextEditorOptionsExt implements theia.TextEditorOptions {
         return undefined;
     }
 
+    get indentSize(): number {
+        if (this._indentSize === 'tabSize') {
+            return this.tabSize;
+        }
+        return this._indentSize;
+    }
+
+    set indentSize(val: number | string | undefined) {
+        const indentSize = this.validateIndentSize(val);
+        if (!indentSize) {
+            return; // ignore invalid values
+        }
+
+        if (typeof indentSize === 'number') {
+            if (this._indentSize === indentSize) {
+                return;
+            }
+            this._indentSize = indentSize;
+        } else if (val === 'tabSize') {
+            this._indentSize = val;
+        }
+        warnOnError(this.proxy.$trySetOptions(this.id, {
+            indentSize
+        }));
+    }
+
+    private validateIndentSize(val: number | string | undefined): number | 'tabSize' | undefined {
+        if (val === 'tabSize') {
+            return 'tabSize';
+        }
+
+        if (typeof val === 'number') {
+            const r = Math.floor(val);
+            return r > 0 ? r : undefined;
+        }
+        if (typeof val === 'string') {
+            const r = parseInt(val, undefined);
+            if (isNaN(r)) {
+                return undefined;
+            }
+            return r > 0 ? r : undefined;
+        }
+        return undefined;
+    }
+
     get insertSpaces(): boolean | string {
         return this._insertSpace;
     }
@@ -395,6 +442,19 @@ export class TextEditorOptionsExt implements theia.TextEditorOptions {
             }
         }
 
+        if (typeof newOptions.indentSize !== 'undefined') {
+            const indentSize = this.validateIndentSize(newOptions.indentSize);
+            if (indentSize === 'tabSize') {
+                hasUpdate = true;
+                configurationUpdate.indentSize = indentSize;
+            } else if (typeof indentSize === 'number' && this._indentSize !== indentSize) {
+                // reflect the new indentSize value immediately
+                this._indentSize = indentSize;
+                hasUpdate = true;
+                configurationUpdate.indentSize = indentSize;
+            }
+        }
+
         if (typeof newOptions.insertSpaces !== 'undefined') {
             const insertSpaces = this.validateInsertSpaces(newOptions.insertSpaces);
             if (insertSpaces === 'auto') {
diff --git a/packages/plugin/src/theia.d.ts b/packages/plugin/src/theia.d.ts
index 3c8d947abdb74..90a9088e684de 100644
--- a/packages/plugin/src/theia.d.ts
+++ b/packages/plugin/src/theia.d.ts
@@ -1909,6 +1909,14 @@ export module '@theia/plugin' {
          */
         tabSize?: number | string;
 
+        /**
+         * The number of spaces to insert when {@link TextEditorOptions.insertSpaces insertSpaces} is true.
+         *
+         * When getting a text editor's options, this property will always be a number (resolved).
+         * When setting a text editor's options, this property is optional and it can be a number or `"tabSize"`.
+         */
+        indentSize?: number | string;
+
         /**
          * When pressing Tab insert {@link TextEditorOptions.tabSize n} spaces.
          * When getting a text editor's options, this property will always be a boolean (resolved).