diff --git a/templates/react-native/src/client.ts.twig b/templates/react-native/src/client.ts.twig
index fc5307ed63..bb9b7fcfaa 100644
--- a/templates/react-native/src/client.ts.twig
+++ b/templates/react-native/src/client.ts.twig
@@ -157,6 +157,19 @@ export type UploadProgress = {
     chunksUploaded: number;
 };
 
+/**
+ * A multipart file part that both React Native networking stacks understand.
+ *
+ * React Native's own fetch reads `uri` natively. Expo's fetch, the global
+ * fetch since Expo SDK 57, ignores `uri` and encodes the body from `bytes()`.
+ */
+export type FilePart = {
+    uri: string;
+    name: string;
+    type: string;
+    bytes: () => Promise<Uint8Array>;
+};
+
 class {{spec.info.title | caseUcfirst}}Exception extends Error {
     code: number;
     response: string;
diff --git a/templates/react-native/src/service.ts.twig b/templates/react-native/src/service.ts.twig
index 5fa7a7a134..1f34f85899 100644
--- a/templates/react-native/src/service.ts.twig
+++ b/templates/react-native/src/service.ts.twig
@@ -1,5 +1,5 @@
 import { Client } from './client';
-import type { Payload } from './client';
+import type { FilePart, Payload } from './client';
 
 export class Service {
     static CHUNK_SIZE = 5 * 1024 * 1024; // 5MB
@@ -24,4 +24,27 @@ export class Service {
 
         return output;
     }
+
+    static filePart(
+        uri: string,
+        name: string,
+        type: string,
+        read: () => Promise<string>,
+    ): FilePart {
+        return {
+            uri,
+            name,
+            type,
+            bytes: async () => Service.decodeBase64(await read()),
+        };
+    }
+
+    static decodeBase64(data: string): Uint8Array {
+        const binary = atob(data);
+        const bytes = new Uint8Array(binary.length);
+        for (let index = 0; index < binary.length; index++) {
+            bytes[index] = binary.charCodeAt(index);
+        }
+        return bytes;
+    }
 }
diff --git a/templates/react-native/src/services/template.ts.twig b/templates/react-native/src/services/template.ts.twig
index 2e112b0dd6..3907ec271b 100644
--- a/templates/react-native/src/services/template.ts.twig
+++ b/templates/react-native/src/services/template.ts.twig
@@ -187,6 +187,16 @@ export class {{ service.name | caseUcfirst }} extends Service {
         const size = {{ parameter.name | caseCamel | escapeKeyword }}.size;
 
         if (size <= Service.CHUNK_SIZE) {
+            payload['{{ parameter.name }}'] = Service.filePart(
+                {{ parameter.name | caseCamel | escapeKeyword }}.uri,
+                {{ parameter.name | caseCamel | escapeKeyword }}.name,
+                {{ parameter.name | caseCamel | escapeKeyword }}.type,
+                () =>
+                    FileSystem.readAsStringAsync({{ parameter.name | caseCamel | escapeKeyword }}.uri, {
+                        encoding: FileSystem.EncodingType.Base64,
+                    }),
+            );
+
             return this.client.call(
                 '{{ method.method.value | caseLower }}',
                 uri,
@@ -267,11 +277,12 @@ export class {{ service.name | caseUcfirst }} extends Service {
                 });
             }
 
-            payload['{{ parameter.name }}'] = {{ '{' }}
-                uri: firstPath,
-                name: {{ parameter.name | caseCamel | escapeKeyword }}.name,
-                type: {{ parameter.name | caseCamel | escapeKeyword }}.type,
-            };
+            payload['{{ parameter.name }}'] = Service.filePart(
+                firstPath,
+                {{ parameter.name | caseCamel | escapeKeyword }}.name,
+                {{ parameter.name | caseCamel | escapeKeyword }}.type,
+                async () => firstChunk,
+            );
 
             response = await this.client.call(
                 '{{ method.method.value | caseLower }}',
@@ -350,11 +361,12 @@ export class {{ service.name | caseUcfirst }} extends Service {
             }
 
             const chunkPayload = { ...payload };
-            chunkPayload['{{ parameter.name }}'] = {{ '{' }}
-                uri: chunkPath,
-                name: {{ parameter.name | caseCamel | escapeKeyword }}.name,
-                type: {{ parameter.name | caseCamel | escapeKeyword }}.type,
-            };
+            chunkPayload['{{ parameter.name }}'] = Service.filePart(
+                chunkPath,
+                {{ parameter.name | caseCamel | escapeKeyword }}.name,
+                {{ parameter.name | caseCamel | escapeKeyword }}.type,
+                async () => chunkData,
+            );
 
             const chunkResponse = await this.client.call(
                 '{{ method.method.value | caseLower }}',
diff --git a/tests/e2e/ReactNativeTest.php b/tests/e2e/ReactNativeTest.php
index de55ec0e6b..aba724e1f2 100644
--- a/tests/e2e/ReactNativeTest.php
+++ b/tests/e2e/ReactNativeTest.php
@@ -29,8 +29,10 @@ final class ReactNativeTest extends Base
         'cp tests/e2e/languages/react-native/index.html tests/e2e/sdks/react-native/index.html',
         'cp tests/e2e/languages/react-native/browser.js tests/e2e/sdks/react-native/browser.js',
         'cp tests/e2e/languages/react-native/rollup.test.config.mjs tests/e2e/sdks/react-native/rollup.test.config.mjs',
-        'mkdir -p tests/e2e/sdks/react-native/shims && cp tests/e2e/languages/react-native/shims/expo-file-system.js tests/e2e/sdks/react-native/shims/expo-file-system.js',
-        'docker run --rm -v $(pwd):/app -w /app/tests/e2e/sdks/react-native mcr.microsoft.com/playwright:v1.59.0-jammy sh -c "npm install && npm install --no-save react-native-web react react-dom @rollup/plugin-alias @rollup/plugin-commonjs @rollup/plugin-node-resolve @rollup/plugin-replace"',
+        'mkdir -p tests/e2e/sdks/react-native/shims && cp tests/e2e/languages/react-native/shims/*.js tests/e2e/sdks/react-native/shims/',
+        'cp tests/resources/file.png tests/resources/large_file.mp4 tests/e2e/sdks/react-native/',
+        'docker run --rm -v $(pwd):/app -w /app/tests/e2e/sdks/react-native mcr.microsoft.com/playwright:v1.59.0-jammy sh -c "npm install && npm install --no-save esbuild expo@57 react-native-web react react-dom @rollup/plugin-alias @rollup/plugin-commonjs @rollup/plugin-node-resolve @rollup/plugin-replace"',
+        'docker run --rm -v $(pwd):/app -w /app/tests/e2e/sdks/react-native mcr.microsoft.com/playwright:v1.59.0-jammy sh -c "npx esbuild node_modules/expo/src/winter/FormData.ts node_modules/expo/src/winter/fetch/RequestUtils.ts --bundle --format=esm --outbase=node_modules/expo/src --outdir=shims/expo"',
         'docker run --rm -v $(pwd):/app -w /app/tests/e2e/sdks/react-native mcr.microsoft.com/playwright:v1.59.0-jammy sh -c "npx rollup -c rollup.test.config.mjs"',
     ];
 
@@ -48,6 +50,10 @@ final class ReactNativeTest extends Base
         ...Base::GENERAL_RESPONSES,
         ...Base::PATH_VALIDATION_RESPONSES,
         ...Base::DOWNLOAD_RESPONSES,
+        ...Base::UPLOAD_RESPONSE,
+        ...Base::LARGE_FILE_RESPONSES,
+        ...Base::UPLOAD_RESPONSE, // Object params
+        ...Base::LARGE_FILE_RESPONSES,
         ...Base::ENUM_RESPONSES,
         ...Base::MODEL_RESPONSES,
         ...Base::OPTIONAL_PARAM_RESPONSES,
diff --git a/tests/e2e/languages/react-native/browser.js b/tests/e2e/languages/react-native/browser.js
index 22162aa277..f8f9808e24 100644
--- a/tests/e2e/languages/react-native/browser.js
+++ b/tests/e2e/languages/react-native/browser.js
@@ -1,3 +1,4 @@
+import './shims/expo-runtime';
 import {
     Client,
     Foo,
@@ -142,6 +143,30 @@ import {
     // Download
     console.log(new TextDecoder().decode(await general.download()));
 
+    // Upload
+    const smallFile = {
+        name: 'file.png',
+        type: 'image/png',
+        size: 38756,
+        uri: 'http://localhost:3000/file.png',
+    };
+    const largeFile = {
+        name: 'large_file.mp4',
+        type: 'video/mp4',
+        size: 16310023,
+        uri: 'http://localhost:3000/large_file.mp4',
+    };
+    response = await general.upload('string', 123, ['string in array'], smallFile);
+    console.log(response.result);
+    response = await general.upload('string', 123, ['string in array'], largeFile);
+    console.log(response.result);
+
+    // Upload (Object params)
+    response = await general.upload({ x: 'string', y: 123, z: ['string in array'], file: smallFile });
+    console.log(response.result);
+    response = await general.upload({ x: 'string', y: 123, z: ['string in array'], file: largeFile });
+    console.log(response.result);
+
     // Enum
     response = await general.enum(MockType.First);
     console.log(response.result);
diff --git a/tests/e2e/languages/react-native/rollup.test.config.mjs b/tests/e2e/languages/react-native/rollup.test.config.mjs
index cc2e90bad7..62d4e843ef 100644
--- a/tests/e2e/languages/react-native/rollup.test.config.mjs
+++ b/tests/e2e/languages/react-native/rollup.test.config.mjs
@@ -50,7 +50,7 @@ export default {
                 outDir: 'dist',
                 rootDir: '.',
             },
-            include: ['src/**/*.ts', 'browser.js'],
+            include: ['src/**/*.ts', 'browser.js', 'shims/**/*.js'],
             exclude: ['node_modules/**', 'dist/**'],
         }),
     ],
diff --git a/tests/e2e/languages/react-native/shims/expo-file-system.js b/tests/e2e/languages/react-native/shims/expo-file-system.js
index 412db8d0a2..e1f39f9ca0 100644
--- a/tests/e2e/languages/react-native/shims/expo-file-system.js
+++ b/tests/e2e/languages/react-native/shims/expo-file-system.js
@@ -1,28 +1,60 @@
-const notImplemented = (name) => () => {
-    throw new Error(
-        `expo-file-system shim: ${name} was called, but uploads are not exercised by this test harness.`
-    );
+// Serves files over HTTP from the test server so the SDK's upload code can
+// read them the way it reads a device file in Expo.
+const written = new Map();
+
+const bytesOf = async (uri) => {
+  if (written.has(uri)) {
+    return written.get(uri);
+  }
+  const response = await fetch(uri);
+  return new Uint8Array(await response.arrayBuffer());
+};
+
+const toBase64 = (bytes) => {
+  let binary = "";
+  for (let index = 0; index < bytes.length; index += 0x8000) {
+    binary += String.fromCharCode(...bytes.subarray(index, index + 0x8000));
+  }
+  return btoa(binary);
+};
+
+export const EncodingType = { UTF8: "utf8", Base64: "base64" };
+export const documentDirectory = "";
+export const cacheDirectory = "";
+
+export const getInfoAsync = async (uri) => {
+  const bytes = await bytesOf(uri);
+  return { exists: true, size: bytes.length, uri };
 };
 
-export const EncodingType = { UTF8: 'utf8', Base64: 'base64' };
-export const documentDirectory = '';
-export const cacheDirectory = '';
+export const readAsStringAsync = async (uri, options = {}) => {
+  const bytes = await bytesOf(uri);
+  const position = options.position ?? 0;
+  const length = options.length ?? bytes.length - position;
+  const slice = bytes.subarray(position, position + length);
+  return options.encoding === EncodingType.Base64
+    ? toBase64(slice)
+    : new TextDecoder().decode(slice);
+};
 
-export const getInfoAsync = notImplemented('getInfoAsync');
-export const readAsStringAsync = notImplemented('readAsStringAsync');
-export const writeAsStringAsync = notImplemented('writeAsStringAsync');
-export const deleteAsync = notImplemented('deleteAsync');
-export const uploadAsync = notImplemented('uploadAsync');
-export const FileSystemUploadType = { BINARY_CONTENT: 0, MULTIPART: 1 };
+export const writeAsStringAsync = async (uri, data, options = {}) => {
+  const bytes =
+    options.encoding === EncodingType.Base64
+      ? Uint8Array.from(atob(data), (character) => character.charCodeAt(0))
+      : new TextEncoder().encode(data);
+  written.set(uri, bytes);
+};
+
+export const deleteAsync = async (uri) => {
+  written.delete(uri);
+};
 
 export default {
-    EncodingType,
-    documentDirectory,
-    cacheDirectory,
-    getInfoAsync,
-    readAsStringAsync,
-    writeAsStringAsync,
-    deleteAsync,
-    uploadAsync,
-    FileSystemUploadType,
+  EncodingType,
+  documentDirectory,
+  cacheDirectory,
+  getInfoAsync,
+  readAsStringAsync,
+  writeAsStringAsync,
+  deleteAsync,
 };
diff --git a/tests/e2e/languages/react-native/shims/expo-runtime.js b/tests/e2e/languages/react-native/shims/expo-runtime.js
new file mode 100644
index 0000000000..480c5a4a6c
--- /dev/null
+++ b/tests/e2e/languages/react-native/shims/expo-runtime.js
@@ -0,0 +1,40 @@
+// Reproduces the part of Expo's native runtime that uploads go through since
+// Expo SDK 57 made expo/fetch the global fetch: React Native's FormData, Expo's
+// FormData patch, and Expo's multipart body encoder. Only the transport is the
+// browser's fetch, sending the bytes Expo would hand to its native request.
+//
+// Expo ships these as TypeScript sources only, so the test build transpiles
+// them out of node_modules with esbuild before bundling.
+import { installFormDataPatch } from "./expo/winter/FormData";
+import {
+  normalizeBodyInitAsync,
+  normalizeHeadersInit,
+  overrideHeaders,
+} from "./expo/winter/fetch/RequestUtils";
+
+class ReactNativeFormData {
+  constructor() {
+    this._parts = [];
+  }
+
+  append(key, value) {
+    this._parts.push([key, value]);
+  }
+}
+
+globalThis.FormData = ReactNativeFormData;
+installFormDataPatch(globalThis.FormData);
+
+const browserFetch = globalThis.fetch.bind(globalThis);
+
+globalThis.fetch = async (input, init = {}) => {
+  if (!(init.body instanceof globalThis.FormData)) {
+    return browserFetch(input, init);
+  }
+  const { body, overriddenHeaders } = await normalizeBodyInitAsync(init.body);
+  const headers = overrideHeaders(
+    normalizeHeadersInit(init.headers),
+    overriddenHeaders ?? [],
+  );
+  return browserFetch(input, { ...init, headers, body });
+};