diff --git a/src/github.ts b/src/github.ts
index 2721948f..8fb3a2b5 100644
--- a/src/github.ts
+++ b/src/github.ts
@@ -827,6 +827,68 @@ export async function getGithubIssueCommentAsync(config: GithubConfig, commentId
   return normalizeGithubIssueComment(data);
 }
 
+// ---------------------------------------------------------------------------
+// Issue assignment helpers
+// ---------------------------------------------------------------------------
+
+export interface AssignGithubIssueResult {
+  ok: boolean;
+  error?: string;
+}
+
+/**
+ * Assign a GitHub user to an issue via `gh issue edit --add-assignee`.
+ *
+ * Uses `runGhDetailedAsync` with rate-limit retry/backoff. On failure returns
+ * `{ ok: false, error: <stderr> }` without throwing.
+ */
+export async function assignGithubIssueAsync(
+  config: GithubConfig,
+  issueNumber: number,
+  assignee: string,
+  retries = 3
+): Promise<AssignGithubIssueResult> {
+  let attempt = 0;
+  let backoff = 500;
+  while (attempt <= retries) {
+    const res = await runGhDetailedAsync(
+      `gh issue edit ${issueNumber} --repo ${config.repo} --add-assignee ${JSON.stringify(assignee)}`
+    );
+    if (res.ok) {
+      return { ok: true };
+    }
+    const stderr = res.stderr || '';
+    // Retry on rate-limit / 403 errors
+    if (/rate limit|403|API rate limit exceeded/i.test(stderr) && attempt < retries) {
+      await new Promise(r => setTimeout(r, backoff));
+      attempt += 1;
+      backoff *= 2;
+      continue;
+    }
+    return { ok: false, error: stderr || `gh issue edit failed with unknown error` };
+  }
+  return { ok: false, error: 'Max retries exceeded' };
+}
+
+/**
+ * Synchronous variant of `assignGithubIssueAsync`. Calls `runGhDetailed`
+ * directly (no retry/backoff). Returns `{ ok: false, error }` on failure
+ * without throwing.
+ */
+export function assignGithubIssue(
+  config: GithubConfig,
+  issueNumber: number,
+  assignee: string
+): AssignGithubIssueResult {
+  const res = runGhDetailed(
+    `gh issue edit ${issueNumber} --repo ${config.repo} --add-assignee ${JSON.stringify(assignee)}`
+  );
+  if (res.ok) {
+    return { ok: true };
+  }
+  return { ok: false, error: res.stderr || `gh issue edit failed with unknown error` };
+}
+
 /**
  * Legacy priority label mapping. Labels like `wl:P0`, `wl:P1`, etc. are mapped
  * to the current priority values for backward compatibility during import.
diff --git a/tests/github-assign-issue.test.ts b/tests/github-assign-issue.test.ts
new file mode 100644
index 00000000..55744470
--- /dev/null
+++ b/tests/github-assign-issue.test.ts
@@ -0,0 +1,225 @@
+/**
+ * Tests for assignGithubIssue and assignGithubIssueAsync helpers in github.ts
+ *
+ * Validates that:
+ * - assignGithubIssueAsync calls `gh issue edit --add-assignee` and returns { ok: true } on success
+ * - assignGithubIssueAsync returns { ok: false, error } on failure without throwing
+ * - assignGithubIssueAsync retries on rate-limit / 403 errors with backoff
+ * - assignGithubIssueAsync returns { ok: false, error: 'Max retries exceeded' } after exhausting retries
+ * - assignGithubIssue (sync) returns { ok: true } on success
+ * - assignGithubIssue (sync) returns { ok: false, error } on failure without throwing
+ * - Both functions construct the correct gh CLI command with repo, issue number, and assignee
+ */
+
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { EventEmitter } from 'events';
+import { Readable, Writable } from 'stream';
+
+// Mock child_process.spawn (async) and child_process.execSync (sync) for
+// the underlying runGhDetailedAsync / runGhDetailed wrappers.
+const { mockSpawn, mockExecSync } = vi.hoisted(() => {
+  return { mockSpawn: vi.fn(), mockExecSync: vi.fn() };
+});
+
+vi.mock('child_process', async (importOriginal) => {
+  const actual = await importOriginal<typeof import('child_process')>();
+  return { ...actual, spawn: mockSpawn, execSync: mockExecSync };
+});
+
+import {
+  assignGithubIssueAsync,
+  assignGithubIssue,
+} from '../src/github.js';
+import type { GithubConfig, AssignGithubIssueResult } from '../src/github.js';
+
+const defaultConfig: GithubConfig = { repo: 'owner/repo', labelPrefix: 'wl:' };
+
+function createMockSpawnImpl(
+  stdout: string,
+  exitCode: number = 0,
+  stderr: string = ''
+) {
+  return (_cmd: string, _args: string[], _opts: any) => {
+    const proc = new EventEmitter() as any;
+    proc.stdin = new Writable({ write: (_c: any, _e: any, cb: () => void) => cb() });
+    proc.stdout = new Readable({
+      read() {
+        this.push(stdout);
+        this.push(null);
+      },
+    });
+    proc.stdout.setEncoding = () => proc.stdout;
+    proc.stderr = new Readable({
+      read() {
+        this.push(stderr);
+        this.push(null);
+      },
+    });
+    proc.stderr.setEncoding = () => proc.stderr;
+    proc.exitCode = exitCode;
+    proc.kill = () => {};
+
+    // Emit close asynchronously to simulate real process
+    setImmediate(() => {
+      proc.emit('close', exitCode);
+    });
+
+    return proc;
+  };
+}
+
+describe('assignGithubIssueAsync', () => {
+  beforeEach(() => {
+    mockSpawn.mockReset();
+  });
+
+  it('returns { ok: true } on successful assignment', async () => {
+    mockSpawn.mockImplementation(createMockSpawnImpl('', 0));
+
+    const result = await assignGithubIssueAsync(defaultConfig, 42, 'copilot');
+
+    expect(result).toEqual({ ok: true });
+    expect(mockSpawn).toHaveBeenCalledTimes(1);
+    // Verify the command contains the correct issue number and assignee
+    const command = mockSpawn.mock.calls[0][1][1]; // spawn('/bin/sh', ['-c', command])
+    expect(command).toContain('gh issue edit 42');
+    expect(command).toContain('--add-assignee');
+    expect(command).toContain('copilot');
+    expect(command).toContain('--repo owner/repo');
+  });
+
+  it('returns { ok: false, error } on gh failure without throwing', async () => {
+    mockSpawn.mockImplementation(
+      createMockSpawnImpl('', 1, 'user copilot is not assignable to this issue')
+    );
+
+    const result = await assignGithubIssueAsync(defaultConfig, 42, 'copilot');
+
+    expect(result.ok).toBe(false);
+    expect(result.error).toContain('copilot is not assignable');
+  });
+
+  it('retries on rate-limit errors', async () => {
+    let callCount = 0;
+    mockSpawn.mockImplementation((_cmd: string, _args: string[], _opts: any) => {
+      callCount++;
+      if (callCount <= 2) {
+        return createMockSpawnImpl('', 1, 'API rate limit exceeded')(_cmd, _args, _opts);
+      }
+      return createMockSpawnImpl('', 0)(_cmd, _args, _opts);
+    });
+
+    const result = await assignGithubIssueAsync(defaultConfig, 42, 'copilot', 3);
+
+    expect(result.ok).toBe(true);
+    expect(mockSpawn).toHaveBeenCalledTimes(3);
+  });
+
+  it('retries on 403 errors', async () => {
+    let callCount = 0;
+    mockSpawn.mockImplementation((_cmd: string, _args: string[], _opts: any) => {
+      callCount++;
+      if (callCount <= 1) {
+        return createMockSpawnImpl('', 1, '403 Forbidden')(_cmd, _args, _opts);
+      }
+      return createMockSpawnImpl('', 0)(_cmd, _args, _opts);
+    });
+
+    const result = await assignGithubIssueAsync(defaultConfig, 42, 'copilot', 3);
+
+    expect(result.ok).toBe(true);
+    expect(mockSpawn).toHaveBeenCalledTimes(2);
+  });
+
+  it('returns error after exhausting retries on persistent rate limit', async () => {
+    mockSpawn.mockImplementation(
+      createMockSpawnImpl('', 1, 'API rate limit exceeded')
+    );
+
+    const result = await assignGithubIssueAsync(defaultConfig, 42, 'copilot', 2);
+
+    expect(result.ok).toBe(false);
+    expect(result.error).toContain('rate limit');
+    // Should have tried 3 times (initial + 2 retries)
+    expect(mockSpawn).toHaveBeenCalledTimes(3);
+  });
+
+  it('does not retry on non-rate-limit failures', async () => {
+    mockSpawn.mockImplementation(
+      createMockSpawnImpl('', 1, 'repository not found')
+    );
+
+    const result = await assignGithubIssueAsync(defaultConfig, 42, 'copilot', 3);
+
+    expect(result.ok).toBe(false);
+    expect(result.error).toContain('repository not found');
+    // Should not retry
+    expect(mockSpawn).toHaveBeenCalledTimes(1);
+  });
+
+  it('returns fallback error when stderr is empty', async () => {
+    mockSpawn.mockImplementation(
+      createMockSpawnImpl('', 1, '')
+    );
+
+    const result = await assignGithubIssueAsync(defaultConfig, 42, 'copilot');
+
+    expect(result.ok).toBe(false);
+    expect(result.error).toBeTruthy();
+  });
+});
+
+describe('assignGithubIssue (sync)', () => {
+  beforeEach(() => {
+    mockExecSync.mockReset();
+  });
+
+  it('returns { ok: true } on successful assignment', () => {
+    // execSync returns stdout as string on success
+    mockExecSync.mockReturnValue('');
+
+    const result = assignGithubIssue(defaultConfig, 42, 'copilot');
+
+    expect(result).toEqual({ ok: true });
+    expect(mockExecSync).toHaveBeenCalledTimes(1);
+  });
+
+  it('returns { ok: false, error } on gh failure without throwing', () => {
+    // execSync throws on non-zero exit code; runGhDetailed catches it
+    const err: any = new Error('Command failed');
+    err.stderr = 'user copilot is not assignable to this issue';
+    err.stdout = '';
+    mockExecSync.mockImplementation(() => { throw err; });
+
+    const result = assignGithubIssue(defaultConfig, 42, 'copilot');
+
+    expect(result.ok).toBe(false);
+    expect(result.error).toContain('copilot is not assignable');
+  });
+
+  it('returns fallback error when stderr is empty on failure', () => {
+    const err: any = new Error('Command failed');
+    err.stderr = '';
+    err.stdout = '';
+    mockExecSync.mockImplementation(() => { throw err; });
+
+    const result = assignGithubIssue(defaultConfig, 42, 'copilot');
+
+    expect(result.ok).toBe(false);
+    expect(result.error).toBeTruthy();
+  });
+
+  it('constructs correct gh command with repo, issue number, and assignee', () => {
+    mockExecSync.mockReturnValue('');
+
+    assignGithubIssue({ repo: 'myorg/myrepo', labelPrefix: 'wl:' }, 123, 'some-user');
+
+    expect(mockExecSync).toHaveBeenCalledTimes(1);
+    // execSync is called with (command, options)
+    const command = mockExecSync.mock.calls[0][0];
+    expect(command).toContain('gh issue edit 123');
+    expect(command).toContain('--add-assignee');
+    expect(command).toContain('some-user');
+    expect(command).toContain('--repo myorg/myrepo');
+  });
+});