diff --git a/src/main.js b/src/main.js
index 2cb1125288f..3ce8dcbe443 100644
--- a/src/main.js
+++ b/src/main.js
@@ -201,30 +201,45 @@ function configureCommandlineSwitchesSync(cliArgs) {
 		SUPPORTED_ELECTRON_SWITCHES.push('force-renderer-accessibility');
 	}
 
+	const SUPPORTED_MAIN_PROCESS_SWITCHES = [
+
+		// Persistently enable proposed api via argv.json: https://github.com/microsoft/vscode/issues/99775
+		'enable-proposed-api'
+	];
+
 	// Read argv config
 	const argvConfig = readArgvConfigSync();
 
-	// Append each flag to Electron
 	Object.keys(argvConfig).forEach(argvKey => {
-		if (SUPPORTED_ELECTRON_SWITCHES.indexOf(argvKey) === -1) {
-			return; // unsupported argv key
-		}
-
 		const argvValue = argvConfig[argvKey];
 
-		// Color profile
-		if (argvKey === 'force-color-profile') {
-			if (argvValue) {
-				app.commandLine.appendSwitch(argvKey, argvValue);
+		// Append Electron flags to Electron
+		if (SUPPORTED_ELECTRON_SWITCHES.indexOf(argvKey) !== -1) {
+			// Color profile
+			if (argvKey === 'force-color-profile') {
+				if (argvValue) {
+					app.commandLine.appendSwitch(argvKey, argvValue);
+				}
+			}
+
+			// Others
+			else if (argvValue === true || argvValue === 'true') {
+				if (argvKey === 'disable-hardware-acceleration') {
+					app.disableHardwareAcceleration(); // needs to be called explicitly
+				} else {
+					app.commandLine.appendSwitch(argvKey);
+				}
 			}
 		}
 
-		// Others
-		else if (argvValue === true || argvValue === 'true') {
-			if (argvKey === 'disable-hardware-acceleration') {
-				app.disableHardwareAcceleration(); // needs to be called explicitly
-			} else {
-				app.commandLine.appendSwitch(argvKey);
+		// Append main process flags to process.argv
+		else if (SUPPORTED_MAIN_PROCESS_SWITCHES.indexOf(argvKey) !== -1) {
+			if (argvKey === 'enable-proposed-api') {
+				if (Array.isArray(argvValue)) {
+					argvValue.forEach(id => id && typeof id === 'string' && process.argv.push('--enable-proposed-api', id));
+				} else {
+					console.error(`Unexpected value for \`enable-proposed-api\` in argv.json. Expected array of extension ids.`);
+				}
 			}
 		}
 	});
diff --git a/src/vs/workbench/electron-sandbox/desktop.contribution.ts b/src/vs/workbench/electron-sandbox/desktop.contribution.ts
index 98a5a69a614..87280ecbcec 100644
--- a/src/vs/workbench/electron-sandbox/desktop.contribution.ts
+++ b/src/vs/workbench/electron-sandbox/desktop.contribution.ts
@@ -343,6 +343,13 @@ import { IJSONSchema } from 'vs/base/common/jsonSchema';
 			'force-color-profile': {
 				type: 'string',
 				markdownDescription: nls.localize('argv.forceColorProfile', 'Allows to override the color profile to use. If you experience colors appear badly, try to set this to `srgb` and restart.')
+			},
+			'enable-proposed-api': {
+				type: 'array',
+				description: nls.localize('argv.enebleProposedApi', "Enable proposed APIs for a list of extension ids (such as \`vscode.git\`). Proposed APIs are unstable and subject to breaking without warning at any time. This should only be set for extension development and testing purposes."),
+				items: {
+					type: 'string'
+				}
 			}
 		}
 	};