diff --git a/packages/vitest/src/node/config/resolveConfig.ts b/packages/vitest/src/node/config/resolveConfig.ts
index 18a050ebe..d549b041c 100644
--- a/packages/vitest/src/node/config/resolveConfig.ts
+++ b/packages/vitest/src/node/config/resolveConfig.ts
@@ -1056,7 +1056,7 @@ export async function resolveConfig(
       configLoader: options.configLoader,
       mode: options.mode || 'test',
       plugins: [
-        CliOverride(cliOptionsCopy),
+        CliOverride(cliOptionsCopy, true),
         ...VitestConfigServer(pluginsHarness),
         ...VitestConfig(pluginsHarness),
         ...VitestCorePlugin(pluginsHarness, options),
diff --git a/packages/vitest/src/node/plugins/cliOverride.ts b/packages/vitest/src/node/plugins/cliOverride.ts
index 9fc05b5b3..1d45311db 100644
--- a/packages/vitest/src/node/plugins/cliOverride.ts
+++ b/packages/vitest/src/node/plugins/cliOverride.ts
@@ -4,7 +4,7 @@ import type { UserConfig } from '../types/config'
 import { deepMerge } from '@vitest/utils/helpers'
 import { mergeConfig } from 'vite'
 
-export function CliOverride(cliOptions: UserConfig): Plugin {
+export function CliOverride(cliOptions: UserConfig, isRootConfig = false): Plugin {
   return {
     // The CLI plugin overwrites config values with CLI options, making them
     // available in the next plugin. We have to do this via plugins because of watch mode.
@@ -20,10 +20,10 @@ export function CliOverride(cliOptions: UserConfig): Plugin {
         // By default, Vite extends arrays, for example, but CLI options should have the priority
         config.test = deepMerge({}, config.test, options)
 
-        // apply browser CLI options only if the config already has the browser config and not disabled manually
-        if (config.test.browser && browser && (config.test.browser.enabled !== false || browser.enabled)) {
+        // Projects must opt into browser mode, but browser options can initialize the root config.
+        if (browser && (config.test.browser || isRootConfig) && (config.test.browser?.enabled !== false || browser.enabled)) {
           config.test.browser = mergeConfig(
-            config.test.browser,
+            config.test.browser || {},
             browser,
           ) as ResolvedBrowserOptions
         }
diff --git a/test/e2e/test/config/browser-configs.test.ts b/test/e2e/test/config/browser-configs.test.ts
index 12511d2ec..b41d43e7d 100644
--- a/test/e2e/test/config/browser-configs.test.ts
+++ b/test/e2e/test/config/browser-configs.test.ts
@@ -132,6 +132,21 @@ test('assigns names as browsers', async () => {
   ])
 })
 
+test('applies programmatic browser options without existing browser config', async () => {
+  const v = await vitest({
+    $cliConfig: {
+      browser: {
+        enabled: true,
+        headless: true,
+        provider: preview(),
+        instances: [{ browser: 'chromium' }],
+      },
+    },
+  })
+
+  expect(v.projects.map(project => project.name)).toEqual(['chromium'])
+})
+
 test('filters projects', async () => {
   const projects = await config({
     project: 'chromium',