diff --git a/extension/src/popup/components/__tests__/org-add-form.test.ts b/extension/src/popup/components/__tests__/org-add-form.test.ts
new file mode 100644
index 0000000..419264b
--- /dev/null
+++ b/extension/src/popup/components/__tests__/org-add-form.test.ts
@@ -0,0 +1,174 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+vi.mock('../../../shared/state', () => ({
+  getState: vi.fn(() => ({ orgContext: 'personal', orgConfigs: [], orgOffline: false })),
+  setState: vi.fn(),
+  sendMessage: vi.fn(),
+  navigate: vi.fn(),
+  escapeHtml: (s: string) => s,
+  popOutToTab: vi.fn(),
+  isInTab: () => false,
+  openVaultTab: vi.fn(),
+}));
+
+import { openOrgAddForm } from '../org-add-form';
+import { sendMessage } from '../../../shared/state';
+
+const send = sendMessage as ReturnType<typeof vi.fn>;
+
+/** Fill all 7 form fields with the given config values. */
+function fillForm(config: {
+  orgId: string; displayName: string; hostType: string;
+  hostUrl: string; repoPath: string; apiToken: string; memberId: string;
+}): void {
+  const f = (name: string) =>
+    document.querySelector<HTMLInputElement | HTMLSelectElement>(`[name="${name}"]`)!;
+  (f('orgId') as HTMLInputElement).value = config.orgId;
+  (f('displayName') as HTMLInputElement).value = config.displayName;
+  (f('hostType') as HTMLSelectElement).value = config.hostType;
+  (f('hostUrl') as HTMLInputElement).value = config.hostUrl;
+  (f('repoPath') as HTMLInputElement).value = config.repoPath;
+  (f('apiToken') as HTMLInputElement).value = config.apiToken;
+  (f('memberId') as HTMLInputElement).value = config.memberId;
+}
+
+const SAMPLE_CONFIG = {
+  orgId: 'acme',
+  displayName: 'Acme Corp',
+  hostType: 'gitea',
+  hostUrl: 'https://git.acme.com',
+  repoPath: 'acme/vault',
+  apiToken: 'tok-secret',
+  memberId: 'alice',
+};
+
+describe('org-add-form', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    document.body.innerHTML = '';
+  });
+
+  it('renders all 7 fields when opened', () => {
+    openOrgAddForm();
+
+    expect(document.querySelector('[name="orgId"]')).toBeTruthy();
+    expect(document.querySelector('[name="displayName"]')).toBeTruthy();
+    expect(document.querySelector('[name="hostType"]')).toBeTruthy();
+    expect(document.querySelector('[name="hostUrl"]')).toBeTruthy();
+    expect(document.querySelector('[name="repoPath"]')).toBeTruthy();
+    expect(document.querySelector('[name="apiToken"]')).toBeTruthy();
+    expect(document.querySelector('[name="memberId"]')).toBeTruthy();
+  });
+
+  it('apiToken field is type=password', () => {
+    openOrgAddForm();
+    const input = document.querySelector<HTMLInputElement>('[name="apiToken"]')!;
+    expect(input.type).toBe('password');
+  });
+
+  it('renders the submit and cancel buttons with stable ids', () => {
+    openOrgAddForm();
+    expect(document.querySelector('#org-add-submit')).toBeTruthy();
+    expect(document.querySelector('#org-add-cancel')).toBeTruthy();
+  });
+
+  it('renders an (initially empty) error slot', () => {
+    openOrgAddForm();
+    const slot = document.querySelector('.org-add-error');
+    expect(slot).toBeTruthy();
+    expect(slot!.textContent).toBe('');
+  });
+
+  it('hostType select has gitea and github options', () => {
+    openOrgAddForm();
+    const sel = document.querySelector<HTMLSelectElement>('[name="hostType"]')!;
+    const values = Array.from(sel.options).map((o) => o.value);
+    expect(values).toContain('gitea');
+    expect(values).toContain('github');
+  });
+
+  it('filling fields + clicking Add sends org_add_config with all 7 values', async () => {
+    send.mockResolvedValueOnce({ ok: true });
+    const onAdded = vi.fn();
+
+    openOrgAddForm(onAdded);
+    fillForm(SAMPLE_CONFIG);
+
+    const form = document.querySelector<HTMLFormElement>('#org-add-form')!;
+    form.dispatchEvent(new Event('submit', { bubbles: true, cancelable: true }));
+    await Promise.resolve();
+    await Promise.resolve();
+
+    expect(send).toHaveBeenCalledWith({
+      type: 'org_add_config',
+      config: SAMPLE_CONFIG,
+    });
+  });
+
+  it('on ok:true removes the overlay and calls onAdded with the orgId', async () => {
+    send.mockResolvedValueOnce({ ok: true });
+    const onAdded = vi.fn();
+
+    openOrgAddForm(onAdded);
+    fillForm(SAMPLE_CONFIG);
+
+    const form = document.querySelector<HTMLFormElement>('#org-add-form')!;
+    form.dispatchEvent(new Event('submit', { bubbles: true, cancelable: true }));
+    await Promise.resolve();
+    await Promise.resolve();
+
+    expect(document.querySelector('#org-add-overlay')).toBeNull();
+    expect(onAdded).toHaveBeenCalledWith('acme');
+  });
+
+  it('on ok:false keeps the overlay open and shows error copy in the error slot', async () => {
+    send.mockResolvedValueOnce({ ok: false, error: 'org_already_configured' });
+
+    openOrgAddForm();
+    fillForm(SAMPLE_CONFIG);
+
+    const form = document.querySelector<HTMLFormElement>('#org-add-form')!;
+    form.dispatchEvent(new Event('submit', { bubbles: true, cancelable: true }));
+    await Promise.resolve();
+    await Promise.resolve();
+
+    // Overlay must still be in the DOM.
+    expect(document.querySelector('#org-add-overlay')).toBeTruthy();
+
+    // The friendly copy for org_already_configured.
+    const slot = document.querySelector('.org-add-error')!;
+    expect(slot.textContent).toContain('already');
+  });
+
+  it('Cancel button removes the overlay without calling sendMessage', async () => {
+    openOrgAddForm();
+
+    const cancel = document.querySelector<HTMLButtonElement>('#org-add-cancel')!;
+    cancel.click();
+    await Promise.resolve();
+
+    expect(document.querySelector('#org-add-overlay')).toBeNull();
+    expect(send).not.toHaveBeenCalled();
+  });
+
+  it('clicking the backdrop removes the overlay without calling sendMessage', async () => {
+    openOrgAddForm();
+
+    const overlay = document.querySelector<HTMLElement>('#org-add-overlay')!;
+    overlay.dispatchEvent(new MouseEvent('click', { bubbles: true }));
+    await Promise.resolve();
+
+    expect(document.querySelector('#org-add-overlay')).toBeNull();
+    expect(send).not.toHaveBeenCalled();
+  });
+
+  it('Esc key removes the overlay without calling sendMessage', async () => {
+    openOrgAddForm();
+
+    document.dispatchEvent(new KeyboardEvent('keydown', { key: 'Escape', bubbles: true }));
+    await Promise.resolve();
+
+    expect(document.querySelector('#org-add-overlay')).toBeNull();
+    expect(send).not.toHaveBeenCalled();
+  });
+});
diff --git a/extension/src/popup/components/org-add-form.ts b/extension/src/popup/components/org-add-form.ts
new file mode 100644
index 0000000..e7d486a
--- /dev/null
+++ b/extension/src/popup/components/org-add-form.ts
@@ -0,0 +1,128 @@
+// org-add-form.ts — Modal form for adding a new org config.
+//
+// Self-contained: appended to document.body so it works in both the popup
+// and the vault sidebar without touching either surface's router.
+//
+// Sends `org_add_config { config: OrgConfig }` on submit and calls the
+// optional `onAdded` callback with the new orgId on success.
+
+import type { OrgConfig } from '../../shared/types';
+import { sendMessage } from '../../shared/state';
+import { lookupErrorCopy } from '../../shared/error-copy';
+
+export function openOrgAddForm(onAdded?: (orgId: string) => void): void {
+  // Build the overlay + form.
+  const overlay = document.createElement('div');
+  overlay.id = 'org-add-overlay';
+  overlay.style.cssText =
+    'position:fixed;inset:0;background:rgba(0,0,0,.5);display:flex;' +
+    'align-items:center;justify-content:center;z-index:9999;';
+
+  const form = document.createElement('form');
+  form.id = 'org-add-form';
+  form.style.cssText =
+    'background:#fff;border-radius:8px;padding:1.5rem;min-width:320px;' +
+    'display:flex;flex-direction:column;gap:.75rem;';
+
+  form.innerHTML = `
+    <h2 style="margin:0 0 .5rem">Add organization</h2>
+
+    <label>Org ID
+      <input name="orgId" type="text" required autocomplete="off" />
+    </label>
+
+    <label>Display name
+      <input name="displayName" type="text" required autocomplete="off" />
+    </label>
+
+    <label>Host type
+      <select name="hostType">
+        <option value="gitea">Gitea</option>
+        <option value="github">GitHub</option>
+      </select>
+    </label>
+
+    <label>Host URL
+      <input name="hostUrl" type="text" required autocomplete="off" placeholder="https://git.example.com" />
+    </label>
+
+    <label>Repo path
+      <input name="repoPath" type="text" required autocomplete="off" placeholder="org/vault" />
+    </label>
+
+    <label>API token
+      <input name="apiToken" type="password" required autocomplete="off" />
+    </label>
+
+    <label>Member ID
+      <input name="memberId" type="text" required autocomplete="off" />
+    </label>
+
+    <div class="org-add-error" style="color:#c00;min-height:1.2em;font-size:.875rem;"></div>
+
+    <div style="display:flex;gap:.5rem;justify-content:flex-end;">
+      <button type="button" id="org-add-cancel">Cancel</button>
+      <button type="submit" id="org-add-submit">Add</button>
+    </div>
+  `;
+
+  overlay.appendChild(form);
+  document.body.appendChild(overlay);
+
+  const errorSlot = form.querySelector('.org-add-error') as HTMLElement;
+
+  function close(): void {
+    overlay.remove();
+  }
+
+  // Cancel button.
+  form.querySelector('#org-add-cancel')!.addEventListener('click', close);
+
+  // Backdrop click.
+  overlay.addEventListener('click', (e) => {
+    if (e.target === overlay) close();
+  });
+
+  // Esc key.
+  function onKeydown(e: KeyboardEvent): void {
+    if (e.key === 'Escape') {
+      close();
+      document.removeEventListener('keydown', onKeydown);
+    }
+  }
+  document.addEventListener('keydown', onKeydown);
+
+  // Clean up the keydown listener when the overlay is removed (cancel/success).
+  const observer = new MutationObserver(() => {
+    if (!document.body.contains(overlay)) {
+      document.removeEventListener('keydown', onKeydown);
+      observer.disconnect();
+    }
+  });
+  observer.observe(document.body, { childList: true });
+
+  // Submit.
+  form.addEventListener('submit', async (e) => {
+    e.preventDefault();
+    errorSlot.textContent = '';
+
+    const data = new FormData(form);
+    const config: OrgConfig = {
+      orgId:       (data.get('orgId')      as string).trim(),
+      displayName: (data.get('displayName') as string).trim(),
+      hostType:    (data.get('hostType')    as 'gitea' | 'github'),
+      hostUrl:     (data.get('hostUrl')     as string).trim(),
+      repoPath:    (data.get('repoPath')    as string).trim(),
+      apiToken:    (data.get('apiToken')    as string).trim(),
+      memberId:    (data.get('memberId')    as string).trim(),
+    };
+
+    const resp = await sendMessage({ type: 'org_add_config', config });
+    if (resp.ok) {
+      close();
+      onAdded?.(config.orgId);
+    } else {
+      errorSlot.textContent = lookupErrorCopy(resp.error ?? '').body;
+    }
+  });
+}
diff --git a/extension/src/popup/components/org-switcher.ts b/extension/src/popup/components/org-switcher.ts
index a2e5a0c..1598aaa 100644
--- a/extension/src/popup/components/org-switcher.ts
+++ b/extension/src/popup/components/org-switcher.ts
@@ -9,6 +9,7 @@
 import type { OrgConfigSummary, OrgManifestEntry, ManifestEntry, ItemId, Collection } from '../../shared/types';
 import { sendMessage, setState, navigate, getState } from '../../shared/state';
 import { messageForList, normalizeOrgEntries } from '../../shared/org-context';
+import { openOrgAddForm } from './org-add-form';
 
 // Module-level teardown (one instance per browser context; popup and vault
 // each have their own module scope).
@@ -35,7 +36,8 @@ export async function renderOrgSwitcher(host: HTMLElement): Promise<void> {
     optionsHtml += `<option value="${org.orgId}"${sel}>${org.displayName}</option>`;
   }
   host.innerHTML =
-    `<select class="org-switcher" aria-label="Vault context">${optionsHtml}</select>`;
+    `<select class="org-switcher" aria-label="Vault context">${optionsHtml}</select>` +
+    `<button class="org-add-btn" type="button" title="Add organization" aria-label="Add organization">&#xFF0B;</button>`;
 
   // 4. Wire the change event.
   const select = host.querySelector('select') as HTMLSelectElement;
@@ -87,6 +89,13 @@ export async function renderOrgSwitcher(host: HTMLElement): Promise<void> {
   };
 
   select.addEventListener('change', handler);
+
+  // 5. Wire the "Add organization" button.
+  const addBtn = host.querySelector('.org-add-btn') as HTMLButtonElement;
+  addBtn.addEventListener('click', () => {
+    openOrgAddForm((_orgId) => { void renderOrgSwitcher(host); });
+  });
+
   _cleanupListener = () => select.removeEventListener('change', handler);
 }