diff --git a/CHANGELOG.md b/CHANGELOG.md
index a7af92eed0..7109514fc8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,10 @@
 
 ## Unreleased
 
+### Features
+
+- Use the optional `react-native-quick-base64` peer dependency for envelope base64 encoding when installed, to improve `captureEnvelope` performance. Falls back to the bundled JS encoder if the package is absent. ([#6314](https://github.com/getsentry/sentry-react-native/pull/6314))
+
 ### Fixes
 
 - Remove unused `React/RCTTextView.h` import that broke iOS builds on React Native 0.87, where the header was removed as part of the legacy architecture cleanup ([#6322](https://github.com/getsentry/sentry-react-native/pull/6322))
diff --git a/packages/core/package.json b/packages/core/package.json
index 793286d98e..c043a40b0c 100644
--- a/packages/core/package.json
+++ b/packages/core/package.json
@@ -70,7 +70,8 @@
   "peerDependencies": {
     "expo": ">=49.0.0",
     "react": ">=17.0.0",
-    "react-native": ">=0.65.0"
+    "react-native": ">=0.65.0",
+    "react-native-quick-base64": ">=3.0.0"
   },
   "dependencies": {
     "@sentry/babel-plugin-component-annotate": "5.3.0",
@@ -130,6 +131,9 @@
   "peerDependenciesMeta": {
     "expo": {
       "optional": true
+    },
+    "react-native-quick-base64": {
+      "optional": true
     }
   }
 }
diff --git a/packages/core/src/js/utils/base64.ts b/packages/core/src/js/utils/base64.ts
new file mode 100644
index 0000000000..18d5857cd9
--- /dev/null
+++ b/packages/core/src/js/utils/base64.ts
@@ -0,0 +1,58 @@
+import { debug } from '@sentry/core';
+
+import { base64StringFromByteArray } from '../vendor';
+
+type FromByteArray = (bytes: Uint8Array, urlSafe?: boolean) => string;
+
+let cachedEncoder: FromByteArray | null = null;
+let resolved = false;
+
+/**
+ * Resolves the base64 encoder once. If the optional peer dependency
+ * `react-native-quick-base64` is installed, its native JSI encoder is used.
+ * Otherwise the bundled JS encoder from `vendor/base64-js` is used.
+ *
+ * The resolution is cached so the require cost is paid at most once.
+ */
+function resolveEncoder(): FromByteArray {
+  if (resolved) {
+    return cachedEncoder ?? base64StringFromByteArray;
+  }
+  resolved = true;
+
+  try {
+    // Optional peer dependency — only loaded if the consumer installed it.
+    // eslint-disable-next-line @typescript-eslint/no-var-requires, import/no-extraneous-dependencies
+    const quickBase64 = require('react-native-quick-base64') as { fromByteArray?: FromByteArray };
+    if (quickBase64 && typeof quickBase64.fromByteArray === 'function') {
+      // Probe the native binding so that a broken native module falls through
+      // to the JS encoder instead of throwing on every envelope.
+      quickBase64.fromByteArray(new Uint8Array([0]));
+      cachedEncoder = quickBase64.fromByteArray;
+      debug.log('Using react-native-quick-base64 for envelope encoding.');
+      return cachedEncoder;
+    }
+  } catch (_e) {
+    // Not installed — fall through to JS encoder.
+  }
+
+  cachedEncoder = base64StringFromByteArray;
+  return cachedEncoder;
+}
+
+/**
+ * Encode a byte array to a base64 string. Prefers the native
+ * `react-native-quick-base64` encoder when available, otherwise uses the
+ * bundled JS implementation.
+ */
+export function encodeToBase64(input: Uint8Array): string {
+  return resolveEncoder()(input);
+}
+
+/**
+ * @internal Test helper. Resets the cached encoder so the next call re-resolves.
+ */
+export function _resetBase64EncoderForTesting(): void {
+  cachedEncoder = null;
+  resolved = false;
+}
diff --git a/packages/core/src/js/wrapper.ts b/packages/core/src/js/wrapper.ts
index d4225740d6..f53cfa5726 100644
--- a/packages/core/src/js/wrapper.ts
+++ b/packages/core/src/js/wrapper.ts
@@ -30,11 +30,11 @@ import type { MobileReplayOptions } from './replay/mobilereplay';
 import type { RequiredKeysUser } from './user';
 
 import { isHardCrash } from './misc';
+import { encodeToBase64 } from './utils/base64';
 import { encodeUTF8 } from './utils/encode';
 import { isTurboModuleEnabled } from './utils/environment';
 import { convertToNormalizedObject } from './utils/normalize';
 import { ReactNativeLibraries } from './utils/rnlibraries';
-import { base64StringFromByteArray } from './vendor';
 import { SDK_VERSION } from './version';
 
 /**
@@ -231,7 +231,7 @@ export const NATIVE: SentryNativeWrapper = {
       envelopeBytes = newBytes;
     }
 
-    await RNSentry.captureEnvelope(base64StringFromByteArray(envelopeBytes), { hardCrashed });
+    await RNSentry.captureEnvelope(encodeToBase64(envelopeBytes), { hardCrashed });
   },
 
   /**
diff --git a/packages/core/test/utils/base64.test.ts b/packages/core/test/utils/base64.test.ts
new file mode 100644
index 0000000000..d294eeab43
--- /dev/null
+++ b/packages/core/test/utils/base64.test.ts
@@ -0,0 +1,69 @@
+import { _resetBase64EncoderForTesting, encodeToBase64 } from '../../src/js/utils/base64';
+
+const quickFromByteArray = jest.fn((bytes: Uint8Array) => Buffer.from(bytes).toString('base64'));
+
+jest.mock(
+  'react-native-quick-base64',
+  () => ({
+    __esModule: true,
+    fromByteArray: quickFromByteArray,
+  }),
+  { virtual: true },
+);
+
+describe('encodeToBase64', () => {
+  beforeEach(() => {
+    _resetBase64EncoderForTesting();
+    quickFromByteArray.mockClear();
+    jest.resetModules();
+  });
+
+  test('uses react-native-quick-base64 when available', () => {
+    // "sentry" => "c2VudHJ5"
+    const result = encodeToBase64(new Uint8Array([0x73, 0x65, 0x6e, 0x74, 0x72, 0x79]));
+    expect(result).toBe('c2VudHJ5');
+    // Probe call during resolution + the actual encode call.
+    expect(quickFromByteArray).toHaveBeenCalledTimes(2);
+    expect(quickFromByteArray).toHaveBeenLastCalledWith(new Uint8Array([0x73, 0x65, 0x6e, 0x74, 0x72, 0x79]));
+  });
+
+  test('falls back to the JS encoder when react-native-quick-base64 is not installed', () => {
+    jest.isolateModules(() => {
+      jest.doMock(
+        'react-native-quick-base64',
+        () => {
+          throw new Error('Cannot find module');
+        },
+        { virtual: true },
+      );
+      // eslint-disable-next-line @typescript-eslint/no-var-requires
+      const {
+        encodeToBase64: isolatedEncode,
+        _resetBase64EncoderForTesting: isolatedReset,
+      } = require('../../src/js/utils/base64');
+      isolatedReset();
+      // "sentry" => "c2VudHJ5"
+      expect(isolatedEncode(new Uint8Array([0x73, 0x65, 0x6e, 0x74, 0x72, 0x79]))).toBe('c2VudHJ5');
+    });
+  });
+
+  test('falls back to the JS encoder when the native binding throws on probe', () => {
+    jest.isolateModules(() => {
+      const brokenFromByteArray = jest.fn(() => {
+        throw new Error('native module not linked');
+      });
+      jest.doMock('react-native-quick-base64', () => ({ __esModule: true, fromByteArray: brokenFromByteArray }), {
+        virtual: true,
+      });
+      // eslint-disable-next-line @typescript-eslint/no-var-requires
+      const {
+        encodeToBase64: isolatedEncode,
+        _resetBase64EncoderForTesting: isolatedReset,
+      } = require('../../src/js/utils/base64');
+      isolatedReset();
+      expect(isolatedEncode(new Uint8Array([0x73, 0x65, 0x6e, 0x74, 0x72, 0x79]))).toBe('c2VudHJ5');
+      // Probe was attempted exactly once; the broken binding is not used for the real encode.
+      expect(brokenFromByteArray).toHaveBeenCalledTimes(1);
+    });
+  });
+});
diff --git a/yarn.lock b/yarn.lock
index 34ecb78c65..0c272a0a0c 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -10931,9 +10931,12 @@ __metadata:
     expo: ">=49.0.0"
     react: ">=17.0.0"
     react-native: ">=0.65.0"
+    react-native-quick-base64: ">=3.0.0"
   peerDependenciesMeta:
     expo:
       optional: true
+    react-native-quick-base64:
+      optional: true
   bin:
     sentry-eas-build-on-complete: scripts/eas-build-hook.js
     sentry-eas-build-on-error: scripts/eas-build-hook.js