diff --git a/dev-packages/browser-integration-tests/suites/public-api/beforeSendTransaction/init.js b/dev-packages/browser-integration-tests/suites/public-api/beforeSendTransaction/init.js
new file mode 100644
index 000000000000..e94e2bd42ab2
--- /dev/null
+++ b/dev-packages/browser-integration-tests/suites/public-api/beforeSendTransaction/init.js
@@ -0,0 +1,23 @@
+import * as Sentry from '@sentry/browser';
+
+window.Sentry = Sentry;
+
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+  integrations: [Sentry.browserTracingIntegration()],
+  beforeSendTransaction: transactionEvent => {
+    const op = transactionEvent.contexts.trace.op;
+    if (op === 'pageload' || op === 'navigation') {
+      // use whatever logic you want to set the name
+      transactionEvent.transaction = 'customName';
+
+      transactionEvent.transaction_info.source = 'route';
+      transactionEvent.contexts.trace.data = {
+        ...transactionEvent.contexts.trace.data,
+        [Sentry.SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]: 'route',
+      };
+    }
+    return transactionEvent;
+  },
+  tracesSampleRate: 1,
+});
diff --git a/dev-packages/browser-integration-tests/suites/public-api/beforeSendTransaction/test.ts b/dev-packages/browser-integration-tests/suites/public-api/beforeSendTransaction/test.ts
new file mode 100644
index 000000000000..14531498e90b
--- /dev/null
+++ b/dev-packages/browser-integration-tests/suites/public-api/beforeSendTransaction/test.ts
@@ -0,0 +1,32 @@
+import { expect } from '@playwright/test';
+import type { Event } from '@sentry/types';
+
+import { SEMANTIC_ATTRIBUTE_SENTRY_SOURCE } from '@sentry/browser';
+import { sentryTest } from '../../../utils/fixtures';
+import { getFirstSentryEnvelopeRequest, shouldSkipTracingTest } from '../../../utils/helpers';
+
+sentryTest(
+  'allows modification of the transaction name and source but overwrites source to custom',
+  async ({ getLocalTestUrl, page }) => {
+    if (shouldSkipTracingTest()) {
+      sentryTest.skip();
+    }
+
+    const url = await getLocalTestUrl({ testDir: __dirname });
+
+    const eventData = await getFirstSentryEnvelopeRequest<Event>(page, url);
+
+    expect(eventData.type).toBe('transaction');
+
+    // user-changed name
+    expect(eventData.transaction).toBe('customName');
+
+    // Despite the user setting the source to 'route', the SDK detects that the txn name was changed
+    // and therefore sets the transaction_info.source to 'custom'. This is not ideal but also not easily changeable.
+    // Given that Relay doesn't differentiate between 'source' and 'route', we'll keep this as-is for now.
+    expect(eventData.transaction_info?.source).toBe('custom');
+
+    // This stays the same but it has no effect on Relay.
+    expect(eventData.contexts?.trace?.data?.[SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]).toBe('route');
+  },
+);