diff --git a/packages/test-helpers/package.json b/packages/test-helpers/package.json
index ca51a79dc9..588bd421b6 100644
--- a/packages/test-helpers/package.json
+++ b/packages/test-helpers/package.json
@@ -18,6 +18,7 @@
   "license": "MIT",
   "dependencies": {
     "@temporalio/common": "workspace:*",
+    "@temporalio/envconfig": "workspace:*",
     "@temporalio/proto": "workspace:*",
     "@temporalio/testing": "workspace:*",
     "@temporalio/worker": "workspace:*",
diff --git a/packages/test-helpers/src/environment.ts b/packages/test-helpers/src/environment.ts
index 2658a01b0b..2bc91327d8 100644
--- a/packages/test-helpers/src/environment.ts
+++ b/packages/test-helpers/src/environment.ts
@@ -1,10 +1,12 @@
 import type { LocalTestWorkflowEnvironmentOptions } from '@temporalio/testing';
 import { workflowInterceptorModules as defaultWorkflowInterceptorModules } from '@temporalio/testing';
+import { loadClientConnectConfig } from '@temporalio/envconfig';
 import type { BundlerPlugin, WorkflowBundleWithSourceMap, BundleOptions } from '@temporalio/worker';
 import { bundleWorkflowCode, DefaultLogger } from '@temporalio/worker';
 import { defineSearchAttributeKey, SearchAttributeType } from '@temporalio/common/lib/search-attributes';
 import { TestWorkflowEnvironment } from './wrappers';
 import { baseBundlerIgnoreModules } from './bundler';
+import { isSet } from './flags';
 
 export const defaultDynamicConfigOptions = [
   'system.enableActivityEagerExecution=true',
@@ -76,14 +78,26 @@ export async function createLocalTestEnvironment(
 }
 
 /**
- * Create a test workflow environment, using an existing server if TEMPORAL_SERVICE_ADDRESS is set,
- * otherwise creating a local one.
+ * Create a test workflow environment.
+ *
+ * Uses envconfig for the test server connection when TEMPORAL_TEST_ENV_CONFIG_SERVER is truthy, uses
+ * TEMPORAL_SERVICE_ADDRESS as a legacy existing-server shortcut when set, otherwise creates a local environment.
  */
 export async function createTestWorkflowEnvironment(
   opts?: LocalTestWorkflowEnvironmentOptions
 ): Promise<TestWorkflowEnvironment> {
   let env: TestWorkflowEnvironment;
-  if (process.env.TEMPORAL_SERVICE_ADDRESS) {
+  if (isSet(process.env.TEMPORAL_TEST_ENV_CONFIG_SERVER, false)) {
+    const { namespace, connectionOptions } = loadClientConnectConfig();
+    const { address, apiKey, metadata, tls } = connectionOptions;
+    env = await TestWorkflowEnvironment.createFromExistingServer({
+      address,
+      namespace,
+      connectionOptions: { apiKey, metadata, tls },
+      client: opts?.client,
+      plugins: opts?.plugins,
+    });
+  } else if (process.env.TEMPORAL_SERVICE_ADDRESS) {
     env = await TestWorkflowEnvironment.createFromExistingServer({
       address: process.env.TEMPORAL_SERVICE_ADDRESS,
       plugins: opts?.plugins,
diff --git a/packages/test-helpers/src/helpers.ts b/packages/test-helpers/src/helpers.ts
index c704764944..d0dd80a104 100644
--- a/packages/test-helpers/src/helpers.ts
+++ b/packages/test-helpers/src/helpers.ts
@@ -73,6 +73,7 @@ export function helpers<TEnv extends AnyTestWorkflowEnvironment = TestWorkflowEn
     async createWorker(workerOpts?: Partial<WorkerOptions>): Promise<Worker> {
       return await Worker.create({
         connection: env.nativeConnection,
+        namespace: env.namespace,
         workflowBundle,
         taskQueue,
         showStackTraceSources: true,
diff --git a/packages/test-helpers/tsconfig.json b/packages/test-helpers/tsconfig.json
index 9cb59c3d55..3f9d6e5a66 100644
--- a/packages/test-helpers/tsconfig.json
+++ b/packages/test-helpers/tsconfig.json
@@ -7,6 +7,7 @@
   "references": [
     { "path": "../client" },
     { "path": "../common" },
+    { "path": "../envconfig" },
     { "path": "../proto" },
     { "path": "../testing" },
     { "path": "../worker" },
diff --git a/packages/test/src/helpers-integration.ts b/packages/test/src/helpers-integration.ts
index cac93b103e..d4180121a0 100644
--- a/packages/test/src/helpers-integration.ts
+++ b/packages/test/src/helpers-integration.ts
@@ -171,7 +171,7 @@ export function helpers(t: ExecutionContext<Context>, env?: TestWorkflowEnvironm
   return {
     ...base,
     async createNativeConnection(opts?: Partial<NativeConnectionOptions>): Promise<NativeConnection> {
-      return await NativeConnection.connect({ address: testEnv.address, ...opts });
+      return await NativeConnection.connect({ ...testEnv.connectionOptions, address: testEnv.address, ...opts });
     },
     async runReplayHistory(
       opts: Partial<ReplayWorkerOptions>,
diff --git a/packages/test/src/test-ephemeral-server.ts b/packages/test/src/test-ephemeral-server.ts
index cdceabe726..d69038b219 100644
--- a/packages/test/src/test-ephemeral-server.ts
+++ b/packages/test/src/test-ephemeral-server.ts
@@ -1,11 +1,14 @@
 import fs from 'fs/promises';
 import { randomUUID } from 'crypto';
+import os from 'os';
+import path from 'path';
 import type { ExecutionContext, TestFn } from 'ava';
 import anyTest from 'ava';
 import type { WorkflowBundle } from '@temporalio/worker';
 import { bundleWorkflowCode } from '@temporalio/worker';
 import { Connection } from '@temporalio/client';
 import { TestWorkflowEnvironment as RealTestWorkflowEnvironment } from '@temporalio/testing';
+import { createTestWorkflowEnvironment } from '@temporalio/test-helpers';
 import {
   Worker,
   TestWorkflowEnvironment,
@@ -80,6 +83,50 @@ test('TestEnvironment sets up dev server and is able to run a single workflow',
   await runSimpleWorkflow(t, testEnv);
 });
 
+test.serial('Shared test harness supports envconfig and legacy existing servers', async (t) => {
+  const namespace = 'envconfig-test';
+  const sourceEnv = await RealTestWorkflowEnvironment.createLocal({ server: { namespace } });
+  const originalTemporalEnv = Object.fromEntries(
+    Object.entries(process.env).filter(([key, value]) => key.startsWith('TEMPORAL_') && value !== undefined)
+  ) as Record<string, string>;
+  let envconfigEnv: TestWorkflowEnvironment | undefined;
+  let legacyEnv: TestWorkflowEnvironment | undefined;
+
+  const setTemporalEnv = (values: Record<string, string>) => {
+    for (const key of Object.keys(process.env)) {
+      if (key.startsWith('TEMPORAL_')) delete process.env[key];
+    }
+    Object.assign(process.env, values);
+  };
+
+  try {
+    setTemporalEnv({
+      TEMPORAL_TEST_ENV_CONFIG_SERVER: 'true',
+      TEMPORAL_CONFIG_FILE: path.join(os.tmpdir(), `missing-temporal-config-${randomUUID()}.toml`),
+      TEMPORAL_ADDRESS: sourceEnv.address,
+      TEMPORAL_NAMESPACE: namespace,
+      TEMPORAL_GRPC_META_TEST_HEADER: 'envconfig-test',
+    });
+
+    envconfigEnv = await createTestWorkflowEnvironment();
+    t.is(envconfigEnv.address, sourceEnv.address);
+    t.is(envconfigEnv.namespace, namespace);
+    t.is(envconfigEnv.connectionOptions.metadata?.['test-header'], 'envconfig-test');
+    await runSimpleWorkflow(t, envconfigEnv);
+    envconfigEnv = undefined;
+
+    setTemporalEnv({ TEMPORAL_SERVICE_ADDRESS: sourceEnv.address });
+    legacyEnv = await createTestWorkflowEnvironment();
+    t.is(legacyEnv.address, sourceEnv.address);
+    await legacyEnv.connection.ensureConnected();
+  } finally {
+    await envconfigEnv?.teardown();
+    await legacyEnv?.teardown();
+    setTemporalEnv(originalTemporalEnv);
+    await sourceEnv.teardown();
+  }
+});
+
 test.todo('TestEnvironment sets up test server with extra args');
 test.todo('TestEnvironment sets up test server with specified port');
 test.todo('TestEnvironment sets up test server with latest version');
diff --git a/packages/testing/src/testing-workflow-environment.ts b/packages/testing/src/testing-workflow-environment.ts
index 14563422be..1d980d5509 100644
--- a/packages/testing/src/testing-workflow-environment.ts
+++ b/packages/testing/src/testing-workflow-environment.ts
@@ -33,14 +33,19 @@ export type TimeSkippingTestWorkflowEnvironmentOptions = {
   plugins?: (ClientPlugin | ConnectionPlugin | NativeConnectionPlugin)[];
 };
 
+type ExistingServerConnectionOptions = Pick<NativeConnectionOptions, 'apiKey' | 'metadata' | 'tls'>;
+
 /**
- * Options for {@link TestWorkflowEnvironment.createExistingServer}
+ * Options for {@link TestWorkflowEnvironment.createFromExistingServer}
+ *
+ * Accepts connection options that can be used for both the client and worker connections.
  */
 export type ExistingServerTestWorkflowEnvironmentOptions = {
   /** If not set, defaults to localhost:7233 */
   address?: string;
   /** If not set, defaults to default */
   namespace?: string;
+  connectionOptions?: ExistingServerConnectionOptions;
   client?: ClientOptionsForTestEnv;
   plugins?: (ClientPlugin | ConnectionPlugin | NativeConnectionPlugin)[];
 };
@@ -99,7 +104,11 @@ export class TestWorkflowEnvironment {
     /**
      * Address used when constructing `connection` and `nativeConnection`
      */
-    public readonly address: string
+    public readonly address: string,
+    /**
+     * Connection options used when constructing `connection` and `nativeConnection`.
+     */
+    public readonly connectionOptions: ExistingServerConnectionOptions
   ) {
     this.connection = connection;
     this.nativeConnection = nativeConnection;
@@ -198,6 +207,7 @@ export class TestWorkflowEnvironment {
   static async createFromExistingServer(
     opts?: ExistingServerTestWorkflowEnvironmentOptions
   ): Promise<TestWorkflowEnvironment> {
+    const { apiKey, metadata, tls } = opts?.connectionOptions ?? {};
     return await this.create({
       server: { type: 'existing' },
       client: opts?.client,
@@ -205,6 +215,7 @@ export class TestWorkflowEnvironment {
       namespace: opts?.namespace ?? 'default',
       supportsTimeSkipping: false,
       address: opts?.address,
+      connectionOptions: { apiKey, metadata, tls },
     });
   }
 
@@ -216,9 +227,10 @@ export class TestWorkflowEnvironment {
       supportsTimeSkipping: boolean;
       namespace?: string;
       address?: string;
+      connectionOptions?: ExistingServerConnectionOptions;
     }
   ): Promise<TestWorkflowEnvironment> {
-    const { supportsTimeSkipping, namespace, ...rest } = opts;
+    const { supportsTimeSkipping, namespace, connectionOptions, ...rest } = opts;
     const optsWithDefaults = addDefaults(filterNullAndUndefined(rest));
 
     let address: string;
@@ -243,12 +255,15 @@ export class TestWorkflowEnvironment {
       server = 'existing';
     }
 
+    const connectionOptionsWithDefaults = { ...(connectionOptions ?? {}), address };
     const nativeConnection = await NativeConnection.connect(<NativeConnectionOptions & InternalConnectionOptions>{
+      ...connectionOptionsWithDefaults,
       address,
       plugins: opts.plugins,
       [InternalConnectionOptionsSymbol]: { supportsTestService: supportsTimeSkipping },
     });
     const connection = await Connection.connect(<ConnectionOptions & InternalConnectionOptions>{
+      ...connectionOptionsWithDefaults,
       address,
       plugins: opts.plugins,
       [InternalConnectionOptionsSymbol]: { supportsTestService: supportsTimeSkipping },
@@ -262,7 +277,8 @@ export class TestWorkflowEnvironment {
       connection,
       nativeConnection,
       namespace,
-      address
+      address,
+      connectionOptionsWithDefaults
     );
   }
 
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 3ce2aa8e1b..c2f44ca121 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -810,6 +810,9 @@ importers:
       '@temporalio/common':
         specifier: workspace:*
         version: link:../common
+      '@temporalio/envconfig':
+        specifier: workspace:*
+        version: link:../envconfig
       '@temporalio/proto':
         specifier: workspace:*
         version: link:../proto