diff --git a/.changeset/fluffy-fishes-remember.md b/.changeset/fluffy-fishes-remember.md
new file mode 100644
index 00000000..02658f58
--- /dev/null
+++ b/.changeset/fluffy-fishes-remember.md
@@ -0,0 +1,5 @@
+---
+'@sebspark/pubsub': minor
+---
+
+Support initiating PubSub with projectId
diff --git a/packages/pubsub/src/lib/client.ts b/packages/pubsub/src/lib/client.ts
index afc9766f..a3d484f3 100644
--- a/packages/pubsub/src/lib/client.ts
+++ b/packages/pubsub/src/lib/client.ts
@@ -1,19 +1,43 @@
 import type { Topic } from '@google-cloud/pubsub'
 import { PubSub } from '@google-cloud/pubsub'
 
-export const pubsub = new PubSub()
+export type ClientConfig = {
+  projectId: string
+}
+
+const localProjectId = 'local'
+const clients: Record<string, PubSub> = {}
+
+const init = ({ projectId }: ClientConfig = { projectId: localProjectId }) => {
+  if (!clients[projectId]) {
+    if (projectId === localProjectId) {
+      // Create a default client when there is no config.
+      clients[projectId] = new PubSub()
+    } else {
+      clients[projectId] = new PubSub({
+        projectId,
+      })
+    }
+  }
+}
 
 export const getOrCreateTopic = async (
   topicName: string,
+  config?: ClientConfig,
   tries = 0,
 ): Promise<Topic> => {
+  // Ensure there is always a client for desired project, as specified in config.
+  init(config)
+
   try {
-    const [t] = await pubsub.topic(topicName).get({ autoCreate: true })
+    const [t] = await clients[config?.projectId || localProjectId]
+      .topic(topicName)
+      .get({ autoCreate: true })
     return t
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
   } catch (err: any) {
     if (err.code && err?.code === 6 && tries < 3) {
-      return getOrCreateTopic(topicName, tries + 1)
+      return getOrCreateTopic(topicName, config, tries + 1)
     } else {
       throw err
     }
diff --git a/packages/pubsub/src/lib/publisher.ts b/packages/pubsub/src/lib/publisher.ts
index af472204..1f8d331d 100644
--- a/packages/pubsub/src/lib/publisher.ts
+++ b/packages/pubsub/src/lib/publisher.ts
@@ -1,4 +1,4 @@
-import { getOrCreateTopic } from './client'
+import { ClientConfig, getOrCreateTopic } from './client'
 
 interface Publisher<T, Headers, raw> {
   (message: T, headers?: Headers, raw?: raw): Promise<string>
@@ -16,9 +16,10 @@ export const publisher =
     Headers extends Record<string, unknown>,
   >(
     topicName: TopicName,
+    config?: ClientConfig,
   ): Publisher<Msg, Headers, boolean> =>
   async (message, headers?, raw?) => {
-    const topic = await getOrCreateTopic(topicName.toString())
+    const topic = await getOrCreateTopic(topicName.toString(), config)
     const msg: PubsubMessage<Msg, Headers> = {
       message,
       headers,
diff --git a/packages/pubsub/src/lib/pubsub.spec.ts b/packages/pubsub/src/lib/pubsub.spec.ts
index 219636c4..02a96669 100644
--- a/packages/pubsub/src/lib/pubsub.spec.ts
+++ b/packages/pubsub/src/lib/pubsub.spec.ts
@@ -65,6 +65,10 @@ const setup = () => {
     off: vi.fn(),
   }
 
+  const mockConfig = {
+    projectId: 'test-project-id',
+  }
+
   mockTopic.get.mockImplementation(async () => [mockTopic])
   mockTopic.publishMessage.mockImplementation(async () => 'ok')
   mockTopic.createSubscription.mockImplementation(async () => [subscription])
@@ -94,6 +98,7 @@ const setup = () => {
     mockTopic,
     subscription,
     pubsub,
+    mockConfig,
     ...testMessage,
   }
 }
@@ -110,8 +115,52 @@ afterAll(() => {
   delete process.env.PUBSUB_PUSH_HOST
 })
 
-it('creates an instance of PubSub', () => {
-  expect(PubSub).toHaveBeenCalled()
+describe('creates an instance of PubSub', () => {
+  describe('without configuration', () => {
+    it('when publishing', async () => {
+      const { createdPubsub, topicData, topicName } = setup()
+
+      await createdPubsub.topic(topicName).publish(topicData)
+
+      expect(PubSub).toHaveBeenCalled()
+    })
+
+    it('when subscribing', async () => {
+      const { createdPubsub, topicName } = setup()
+
+      await createdPubsub.topic(topicName).subscribe({
+        subscriberName: 'gateway',
+        onSuccess: () => undefined,
+      })
+
+      expect(PubSub).toHaveBeenCalled()
+    })
+  })
+
+  describe('with projectId when passed config', () => {
+    it('when publishing', async () => {
+      const { createdPubsub, mockConfig, topicData, topicName } = setup()
+
+      await createdPubsub.topic(topicName, mockConfig).publish(topicData)
+
+      expect(PubSub).toHaveBeenCalledWith({
+        projectId: mockConfig.projectId,
+      })
+    })
+
+    it('when subscribing', async () => {
+      const { createdPubsub, mockConfig, topicName } = setup()
+
+      await createdPubsub.topic(topicName, mockConfig).subscribe({
+        subscriberName: 'gateway',
+        onSuccess: () => undefined,
+      })
+
+      expect(PubSub).toHaveBeenCalledWith({
+        projectId: mockConfig.projectId,
+      })
+    })
+  })
 })
 
 describe('#topic', () => {
diff --git a/packages/pubsub/src/lib/pubsub.ts b/packages/pubsub/src/lib/pubsub.ts
index 6e52a092..c59e5ea2 100644
--- a/packages/pubsub/src/lib/pubsub.ts
+++ b/packages/pubsub/src/lib/pubsub.ts
@@ -1,3 +1,4 @@
+import { ClientConfig } from './client'
 import { publisher } from './publisher'
 import type { Subscriber, SubscriberHandler, Unsubscriber } from './subscriber'
 import { subscriber } from './subscriber'
@@ -22,17 +23,24 @@ export const createPubsub = <
 >() => {
   type TopicName = keyof Topics
 
-  const topic = (name: TopicName): PubSubTopic<Topics[TopicName], Topics> => {
+  const topic = (
+    name: TopicName,
+    config?: ClientConfig,
+  ): PubSubTopic<Topics[TopicName], Topics> => {
     return {
       publish: publisher<Topics[TopicName], TopicName, Record<string, unknown>>(
         name,
+        config,
       ),
-      subscribe: subscriber<Topics[TopicName], TopicName>(name),
+      subscribe: subscriber<Topics[TopicName], TopicName>(name, config),
       name: name,
     }
   }
 
-  const subscribeToMultipleAs = (name: SubscriberName) => {
+  const subscribeToMultipleAs = (
+    name: SubscriberName,
+    config: ClientConfig,
+  ) => {
     const promises: Promise<Unsubscriber>[] = []
     const obj = {
       wait: async () => await Promise.all(promises),
@@ -41,7 +49,7 @@ export const createPubsub = <
         { onSuccess, onError }: SubscriberHandler<Topics[TopicName]>,
       ) => {
         promises.push(
-          topic(topicName.toString()).subscribe({
+          topic(topicName.toString(), config).subscribe({
             subscriberName: name,
             onSuccess,
             onError,
diff --git a/packages/pubsub/src/lib/subscriber.ts b/packages/pubsub/src/lib/subscriber.ts
index 89fa434c..b4bd67fd 100644
--- a/packages/pubsub/src/lib/subscriber.ts
+++ b/packages/pubsub/src/lib/subscriber.ts
@@ -4,7 +4,7 @@ import type {
   Subscription,
   Topic,
 } from '@google-cloud/pubsub'
-import { getOrCreateTopic } from './client'
+import { ClientConfig, getOrCreateTopic } from './client'
 
 const ALREADY_EXISTS_ERROR = '6 ALREADY_EXISTS'
 
@@ -145,9 +145,10 @@ const createOrGetSubscription = async (
 export const subscriber =
   <Msg, TopicName extends string | number | symbol>(
     topicName: TopicName,
+    config?: ClientConfig,
   ): Subscriber<Msg> =>
   async ({ subscriberName, onSuccess, onError }) => {
-    const topic = await getOrCreateTopic(topicName.toString())
+    const topic = await getOrCreateTopic(topicName.toString(), config)
     const subscriptionName = `${topicName.toString()}.${subscriberName}`
     const subscription = await createOrGetSubscription(subscriptionName, topic)
     const messageHandler = async (message: Message) => {