diff --git a/doc/api/test.md b/doc/api/test.md
index f88d3542f954bf7..662f7176c0f4a88 100644
--- a/doc/api/test.md
+++ b/doc/api/test.md
@@ -466,6 +466,15 @@ each other in ways that are not possible when isolation is enabled. For example,
 if a test relies on global state, it is possible for that state to be modified
 by a test originating from another file.
 
+## Environment Variables
+
+### `NODE_TEST_WORKER_ID`
+
+when running the test in parallel using the `--experimental-test-isolation=process`
+flag, this environment variable will be set to a number between 1 to N (where N is the
+number of files). When running the test in isolation using the
+`--experimental-test-isolation=none` flag, this environment variable will be set to `1`.
+
 ## Collecting code coverage
 
 > Stability: 1 - Experimental
diff --git a/lib/internal/test_runner/runner.js b/lib/internal/test_runner/runner.js
index 43a62b5b4307e4e..9f54ed0a6d9415c 100644
--- a/lib/internal/test_runner/runner.js
+++ b/lib/internal/test_runner/runner.js
@@ -358,14 +358,14 @@ class FileTest extends Test {
   }
 }
 
-function runTestFile(path, filesWatcher, opts) {
+function runTestFile(path, filesWatcher, opts, workerId = 1) {
   const watchMode = filesWatcher != null;
   const testPath = path === kIsolatedProcessName ? '' : path;
   const testOpts = { __proto__: null, signal: opts.signal };
   const subtest = opts.root.createSubtest(FileTest, testPath, testOpts, async (t) => {
     const args = getRunArgs(path, opts);
     const stdio = ['pipe', 'pipe', 'pipe'];
-    const env = { __proto__: null, ...process.env, NODE_TEST_CONTEXT: 'child-v8' };
+    const env = { __proto__: null, ...process.env, NODE_TEST_CONTEXT: 'child-v8', NODE_TEST_WORKER_ID: workerId };
     if (watchMode) {
       stdio.push('ipc');
       env.WATCH_REPORT_DEPENDENCIES = '1';
@@ -724,8 +724,10 @@ function run(options = kEmptyObject) {
     runFiles = () => {
       root.harness.bootstrapPromise = null;
       root.harness.buildPromise = null;
+      let workerId = 1;
       return SafePromiseAllSettledReturnVoid(testFiles, (path) => {
-        const subtest = runTestFile(path, filesWatcher, opts);
+        const subtest = runTestFile(path, filesWatcher, opts, workerId);
+        workerId++;
         filesWatcher?.runningSubtests.set(path, subtest);
         return subtest;
       });
@@ -766,6 +768,7 @@ function run(options = kEmptyObject) {
 
             root.entryFile = resolve(testFile);
             debug('loading test file:', fileURL.href);
+            process.env.NODE_TEST_WORKER_ID = 1;
             try {
               await cascadedLoader.import(fileURL, parent, { __proto__: null });
             } catch (err) {
diff --git a/test/fixtures/test-runner/NODE_TEST_WORKER_ID/1.test.js b/test/fixtures/test-runner/NODE_TEST_WORKER_ID/1.test.js
new file mode 100644
index 000000000000000..5680299a7554c49
--- /dev/null
+++ b/test/fixtures/test-runner/NODE_TEST_WORKER_ID/1.test.js
@@ -0,0 +1,7 @@
+// This file tests the `NODE_TEST_WORKER_ID` feature.
+// The test logic is implemented in `test/parallel/test-runner-cli.js`.
+const test = require('node:test');
+
+test('test1', t => {
+    console.log('NODE_TEST_WORKER_ID', process.env.NODE_TEST_WORKER_ID)
+});
\ No newline at end of file
diff --git a/test/fixtures/test-runner/NODE_TEST_WORKER_ID/2.test.js b/test/fixtures/test-runner/NODE_TEST_WORKER_ID/2.test.js
new file mode 100644
index 000000000000000..51e0b63dbc29525
--- /dev/null
+++ b/test/fixtures/test-runner/NODE_TEST_WORKER_ID/2.test.js
@@ -0,0 +1,7 @@
+// This file tests the `NODE_TEST_WORKER_ID` feature.
+// The test logic is implemented in `test/parallel/test-runner-cli.js`.
+const test = require('node:test');
+
+test('test2', t => {
+    console.log('NODE_TEST_WORKER_ID', process.env.NODE_TEST_WORKER_ID)
+});
\ No newline at end of file
diff --git a/test/fixtures/test-runner/NODE_TEST_WORKER_ID/3.test.js b/test/fixtures/test-runner/NODE_TEST_WORKER_ID/3.test.js
new file mode 100644
index 000000000000000..27edc8f2d8213b6
--- /dev/null
+++ b/test/fixtures/test-runner/NODE_TEST_WORKER_ID/3.test.js
@@ -0,0 +1,7 @@
+// This file tests the `NODE_TEST_WORKER_ID` feature.
+// The test logic is implemented in `test/parallel/test-runner-cli.js`.
+const test = require('node:test');
+
+test('test3', t => {
+    console.log('NODE_TEST_WORKER_ID', process.env.NODE_TEST_WORKER_ID)
+});
\ No newline at end of file
diff --git a/test/fixtures/test-runner/NODE_TEST_WORKER_ID/4.test.js b/test/fixtures/test-runner/NODE_TEST_WORKER_ID/4.test.js
new file mode 100644
index 000000000000000..9c39b30ec02759a
--- /dev/null
+++ b/test/fixtures/test-runner/NODE_TEST_WORKER_ID/4.test.js
@@ -0,0 +1,7 @@
+// This file tests the `NODE_TEST_WORKER_ID` feature.
+// The test logic is implemented in `test/parallel/test-runner-cli.js`.
+const test = require('node:test');
+
+test('test4', t => {
+    console.log('NODE_TEST_WORKER_ID', process.env.NODE_TEST_WORKER_ID)
+});
\ No newline at end of file
diff --git a/test/parallel/test-runner-cli.js b/test/parallel/test-runner-cli.js
index 3e8e14b747a22f1..017b9fff9790036 100644
--- a/test/parallel/test-runner-cli.js
+++ b/test/parallel/test-runner-cli.js
@@ -428,3 +428,31 @@ for (const isolation of ['none', 'process']) {
   assert.strictEqual(child.status, 0);
   assert.strictEqual(child.signal, null);
 }
+
+{
+  const args = ['--test', '--experimental-test-isolation=process'];
+  const child = spawnSync(process.execPath, args, { cwd: join(testFixtures, 'NODE_TEST_WORKER_ID') });
+
+  assert.strictEqual(child.stderr.toString(), '');
+  const stdout = child.stdout.toString();
+
+  assert.match(stdout, /NODE_TEST_WORKER_ID 1/);
+  assert.match(stdout, /NODE_TEST_WORKER_ID 2/);
+  assert.match(stdout, /NODE_TEST_WORKER_ID 3/);
+  assert.match(stdout, /NODE_TEST_WORKER_ID 4/);
+
+  assert.strictEqual(child.status, 0);
+}
+
+{
+  const args = ['--test', '--experimental-test-isolation=none'];
+  const child = spawnSync(process.execPath, args, { cwd: join(testFixtures, 'NODE_TEST_WORKER_ID') });
+
+  assert.strictEqual(child.stderr.toString(), '');
+  const stdout = child.stdout.toString();
+  const regex = /NODE_TEST_WORKER_ID 1/g;
+  const result = stdout.match(regex);
+
+  assert.strictEqual(result.length, 4);
+  assert.strictEqual(child.status, 0);
+}