diff --git a/packages/core/src/baseclient.ts b/packages/core/src/baseclient.ts
index 3f365f111ed9..ef5635f98541 100644
--- a/packages/core/src/baseclient.ts
+++ b/packages/core/src/baseclient.ts
@@ -476,7 +476,7 @@ export abstract class BaseClient<O extends ClientOptions> implements Client<O> {
       return null;
     }
 
-    const normalized = {
+    const normalized: Event = {
       ...event,
       ...(event.breadcrumbs && {
         breadcrumbs: event.breadcrumbs.map(b => ({
@@ -496,6 +496,7 @@ export abstract class BaseClient<O extends ClientOptions> implements Client<O> {
         extra: normalize(event.extra, depth, maxBreadth),
       }),
     };
+
     // event.contexts.trace stores information about a Transaction. Similarly,
     // event.spans[] stores information about child Spans. Given that a
     // Transaction is conceptually a Span, normalization should apply to both
@@ -504,8 +505,24 @@ export abstract class BaseClient<O extends ClientOptions> implements Client<O> {
     // so this block overwrites the normalized event to add back the original
     // Transaction information prior to normalization.
     if (event.contexts && event.contexts.trace) {
-      // eslint-disable-next-line @typescript-eslint/no-unsafe-member-access
+      normalized.contexts = {};
       normalized.contexts.trace = event.contexts.trace;
+
+      // event.contexts.trace.data may contain circular/dangerous data so we need to normalize it
+      if (event.contexts.trace.data) {
+        normalized.contexts.trace.data = normalize(event.contexts.trace.data, depth, maxBreadth);
+      }
+    }
+
+    // event.spans[].data may contain circular/dangerous data so we need to normalize it
+    if (event.spans) {
+      normalized.spans = event.spans.map(span => {
+        // We cannot use the spread operator here because `toJSON` on `span` is non-enumerable
+        if (span.data) {
+          span.data = normalize(span.data, depth, maxBreadth);
+        }
+        return span;
+      });
     }
 
     normalized.sdkProcessingMetadata = { ...normalized.sdkProcessingMetadata, baseClientNormalized: true };
diff --git a/packages/integration-tests/suites/public-api/startTransaction/circular_data/subject.js b/packages/integration-tests/suites/public-api/startTransaction/circular_data/subject.js
new file mode 100644
index 000000000000..50f8cef000be
--- /dev/null
+++ b/packages/integration-tests/suites/public-api/startTransaction/circular_data/subject.js
@@ -0,0 +1,11 @@
+const chicken = {};
+const egg = { contains: chicken };
+chicken.lays = egg;
+
+const circularObject = chicken;
+
+const transaction = Sentry.startTransaction({ name: 'circular_object_test_transaction', data: circularObject });
+const span = transaction.startChild({ op: 'circular_object_test_span', data: circularObject });
+
+span.finish();
+transaction.finish();
diff --git a/packages/integration-tests/suites/public-api/startTransaction/circular_data/test.ts b/packages/integration-tests/suites/public-api/startTransaction/circular_data/test.ts
new file mode 100644
index 000000000000..7ad0ec532fb7
--- /dev/null
+++ b/packages/integration-tests/suites/public-api/startTransaction/circular_data/test.ts
@@ -0,0 +1,26 @@
+import { expect } from '@playwright/test';
+import { Event } from '@sentry/types';
+
+import { sentryTest } from '../../../../utils/fixtures';
+import { getFirstSentryEnvelopeRequest } from '../../../../utils/helpers';
+
+sentryTest('should be able to handle circular data', async ({ getLocalTestPath, page }) => {
+  const url = await getLocalTestPath({ testDir: __dirname });
+  const eventData = await getFirstSentryEnvelopeRequest<Event>(page, url);
+
+  expect(eventData.type).toBe('transaction');
+  expect(eventData.transaction).toBe('circular_object_test_transaction');
+
+  expect(eventData.contexts).toMatchObject({
+    trace: {
+      data: { lays: { contains: '[Circular ~]' } },
+    },
+  });
+
+  expect(eventData?.spans?.[0]).toMatchObject({
+    data: { lays: { contains: '[Circular ~]' } },
+    op: 'circular_object_test_span',
+  });
+
+  await new Promise(resolve => setTimeout(resolve, 2000));
+});
diff --git a/packages/integration-tests/suites/public-api/startTransaction/init.js b/packages/integration-tests/suites/public-api/startTransaction/init.js
index b326cc489bde..0aadc7c39b84 100644
--- a/packages/integration-tests/suites/public-api/startTransaction/init.js
+++ b/packages/integration-tests/suites/public-api/startTransaction/init.js
@@ -7,4 +7,5 @@ window.Sentry = Sentry;
 Sentry.init({
   dsn: 'https://public@dsn.ingest.sentry.io/1337',
   tracesSampleRate: 1.0,
+  normalizeDepth: 10,
 });