diff --git a/lib/internal/test_runner/coverage.js b/lib/internal/test_runner/coverage.js
index 8fa9c872568d1e..577ce15f147d03 100644
--- a/lib/internal/test_runner/coverage.js
+++ b/lib/internal/test_runner/coverage.js
@@ -533,6 +533,8 @@ function setupCoverage(options) {
     return null;
   }
 
+  internalBinding('profiler').startCoverage();
+
   // Ensure that NODE_V8_COVERAGE is set so that coverage can propagate to
   // child processes.
   process.env.NODE_V8_COVERAGE = coverageDirectory;
diff --git a/lib/internal/test_runner/runner.js b/lib/internal/test_runner/runner.js
index 2033ac16e8ea49..ec0677831c373a 100644
--- a/lib/internal/test_runner/runner.js
+++ b/lib/internal/test_runner/runner.js
@@ -805,6 +805,8 @@ function run(options = kEmptyObject) {
       coverageExcludeGlobs = [coverageExcludeGlobs];
     }
     validateStringArray(coverageExcludeGlobs, 'options.coverageExcludeGlobs');
+  } else if (coverage) {
+    coverageExcludeGlobs = [kDefaultPattern];
   }
   if (coverageIncludeGlobs != null) {
     if (!ArrayIsArray(coverageIncludeGlobs)) {
diff --git a/src/inspector_profiler.cc b/src/inspector_profiler.cc
index 28653a3939daef..559b4fd27d56ab 100644
--- a/src/inspector_profiler.cc
+++ b/src/inspector_profiler.cc
@@ -548,6 +548,30 @@ static void SetSourceMapCacheGetter(const FunctionCallbackInfo<Value>& args) {
   env->set_source_map_cache_getter(args[0].As<Function>());
 }
 
+static void StartCoverage(const FunctionCallbackInfo<Value>& args) {
+  Environment* env = Environment::GetCurrent(args);
+
+  Debug(env,
+        DebugCategory::INSPECTOR_PROFILER,
+        "StartCoverage, connection %s nullptr\n",
+        env->coverage_connection() == nullptr ? "==" : "!=");
+
+  if (env->coverage_connection() != nullptr) {
+    return;
+  }
+
+  // The parent of `--test --test-isolation=process` intentionally has no
+  // inspector (see Environment::should_create_inspector); workers handle
+  // coverage themselves. Without an inspector, V8CoverageConnection would
+  // get a null session and crash on the first DispatchMessage.
+  if (!env->should_create_inspector()) {
+    return;
+  }
+
+  env->set_coverage_connection(std::make_unique<V8CoverageConnection>(env));
+  env->coverage_connection()->Start();
+}
+
 static void TakeCoverage(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
   V8CoverageConnection* connection = env->coverage_connection();
@@ -601,6 +625,7 @@ static void Initialize(Local<Object> target,
   SetMethod(context, target, "setCoverageDirectory", SetCoverageDirectory);
   SetMethod(
       context, target, "setSourceMapCacheGetter", SetSourceMapCacheGetter);
+  SetMethod(context, target, "startCoverage", StartCoverage);
   SetMethod(context, target, "takeCoverage", TakeCoverage);
   SetMethod(context, target, "stopCoverage", StopCoverage);
   SetMethod(context, target, "endCoverage", EndCoverage);
@@ -609,6 +634,7 @@ static void Initialize(Local<Object> target,
 void RegisterExternalReferences(ExternalReferenceRegistry* registry) {
   registry->Register(SetCoverageDirectory);
   registry->Register(SetSourceMapCacheGetter);
+  registry->Register(StartCoverage);
   registry->Register(TakeCoverage);
   registry->Register(StopCoverage);
   registry->Register(EndCoverage);
diff --git a/test/fixtures/test-runner/coverage-isolation-none/src/foo.mjs b/test/fixtures/test-runner/coverage-isolation-none/src/foo.mjs
new file mode 100644
index 00000000000000..f6a50e85a9d412
--- /dev/null
+++ b/test/fixtures/test-runner/coverage-isolation-none/src/foo.mjs
@@ -0,0 +1,11 @@
+export function add(a, b) {
+  return a + b;
+}
+
+export function sub(a, b) {
+  return a - b;
+}
+
+export function unused() {
+  return 'unused';
+}
diff --git a/test/fixtures/test-runner/coverage-isolation-none/tests/foo.test.mjs b/test/fixtures/test-runner/coverage-isolation-none/tests/foo.test.mjs
new file mode 100644
index 00000000000000..efbccddc87412b
--- /dev/null
+++ b/test/fixtures/test-runner/coverage-isolation-none/tests/foo.test.mjs
@@ -0,0 +1,11 @@
+import test from 'node:test';
+import assert from 'node:assert';
+import { add, sub } from '../src/foo.mjs';
+
+test('add', () => {
+  assert.strictEqual(add(2, 3), 5);
+});
+
+test('sub', () => {
+  assert.strictEqual(sub(5, 3), 2);
+});
diff --git a/test/parallel/test-runner-coverage-isolation-none-api.mjs b/test/parallel/test-runner-coverage-isolation-none-api.mjs
new file mode 100644
index 00000000000000..08417e5dc3a1b6
--- /dev/null
+++ b/test/parallel/test-runner-coverage-isolation-none-api.mjs
@@ -0,0 +1,92 @@
+import * as common from '../common/index.mjs';
+import { before, describe, it, run } from 'node:test';
+import assert from 'node:assert';
+import { spawnSync } from 'node:child_process';
+import { cp, writeFile } from 'node:fs/promises';
+import { join, sep } from 'node:path';
+import tmpdir from '../common/tmpdir.js';
+import fixtures from '../common/fixtures.js';
+
+const skipIfNoInspector = {
+  skip: !process.features.inspector ? 'inspector disabled' : false,
+};
+
+tmpdir.refresh();
+
+async function setupFixtures() {
+  const fixtureDir = fixtures.path('test-runner', 'coverage-isolation-none');
+  await cp(fixtureDir, tmpdir.path, { recursive: true });
+}
+
+describe('run() coverage with isolation: none', skipIfNoInspector, () => {
+  before(async () => {
+    await setupFixtures();
+  });
+
+  for (const isolation of ['none', 'process']) {
+    it(`reports src coverage and excludes test files by default (isolation=${isolation})`, async () => {
+      const stream = run({
+        files: [join(tmpdir.path, 'tests', 'foo.test.mjs')],
+        coverage: true,
+        isolation,
+        cwd: tmpdir.path,
+      });
+      stream.on('test:fail', common.mustNotCall());
+
+      let summary;
+      stream.on('test:coverage', common.mustCall(({ summary: s }) => {
+        summary = s;
+      }));
+      // eslint-disable-next-line no-unused-vars
+      for await (const _ of stream);
+
+      assert.ok(summary, 'test:coverage event must fire');
+      const paths = summary.files.map((f) => f.path);
+      assert.ok(
+        paths.length > 0,
+        `coverage files must be reported (isolation=${isolation}); got ${JSON.stringify(paths)}`,
+      );
+      assert.ok(
+        paths.some((p) => p.endsWith(`src${sep}foo.mjs`)),
+        `expected src/foo.mjs to be present (isolation=${isolation}); got ${JSON.stringify(paths)}`,
+      );
+      assert.ok(
+        paths.every((p) => !p.endsWith('foo.test.mjs')),
+        `expected foo.test.mjs to be excluded by default (isolation=${isolation}); got ${JSON.stringify(paths)}`,
+      );
+    });
+  }
+
+  it('is idempotent when --experimental-test-coverage is also passed', async () => {
+    const runnerPath = join(tmpdir.path, 'runner.mjs');
+    await writeFile(runnerPath, `\
+import { run } from 'node:test';
+import { join } from 'node:path';
+
+const stream = run({
+  files: [join(import.meta.dirname, 'tests', 'foo.test.mjs')],
+  coverage: true,
+  isolation: 'none',
+  cwd: import.meta.dirname,
+});
+stream.on('test:fail', () => process.exit(10));
+let summary;
+stream.on('test:coverage', (event) => { summary = event.summary; });
+for await (const _ of stream);
+if (!summary || summary.files.length === 0) process.exit(11);
+const hasSrc = summary.files.some((f) => f.path.endsWith('foo.mjs') && !f.path.endsWith('foo.test.mjs'));
+const hasTest = summary.files.some((f) => f.path.endsWith('foo.test.mjs'));
+if (!hasSrc) process.exit(12);
+if (hasTest) process.exit(13);
+`);
+    const result = spawnSync(process.execPath, [
+      '--experimental-test-coverage',
+      runnerPath,
+    ], { cwd: tmpdir.path });
+    assert.strictEqual(
+      result.status,
+      0,
+      `exited with ${result.status}\nstderr: ${result.stderr}\nstdout: ${result.stdout}`,
+    );
+  });
+});
diff --git a/test/parallel/test-runner-run-coverage.mjs b/test/parallel/test-runner-run-coverage.mjs
index 15fcfef5238843..89a9da2a179e44 100644
--- a/test/parallel/test-runner-run-coverage.mjs
+++ b/test/parallel/test-runner-run-coverage.mjs
@@ -123,6 +123,7 @@ describe('require(\'node:test\').run coverage settings', { concurrency: true },
       const stream = run({
         files,
         coverage: true,
+        coverageExcludeGlobs: '!test/**',
         coverageIncludeGlobs: ['test/fixtures/test-runner/coverage.js', 'test/*/v8-coverage/throw.js'],
       });
       stream.on('test:fail', common.mustNotCall());
@@ -157,7 +158,14 @@ describe('require(\'node:test\').run coverage settings', { concurrency: true },
       const thresholdErrors = [];
       const originalExitCode = process.exitCode;
       assert.notStrictEqual(originalExitCode, 1);
-      const stream = run({ files, coverage: true, lineCoverage: 99, branchCoverage: 99, functionCoverage: 99 });
+      const stream = run({
+        files,
+        coverage: true,
+        coverageExcludeGlobs: '!test/**',
+        lineCoverage: 99,
+        branchCoverage: 99,
+        functionCoverage: 99,
+      });
       stream.on('test:fail', common.mustNotCall());
       stream.on('test:pass', common.mustCall(1));
       stream.on('test:diagnostic', ({ message }) => {