diff --git a/apps/web/src/app/(authenticated)/settings/workspaces/[id]/page.test.tsx b/apps/web/src/app/(authenticated)/settings/workspaces/[id]/page.test.tsx
new file mode 100644
index 0000000..c427cb9
--- /dev/null
+++ b/apps/web/src/app/(authenticated)/settings/workspaces/[id]/page.test.tsx
@@ -0,0 +1,64 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { render, screen, waitFor } from "@testing-library/react";
+import WorkspaceDetailPage from "./page";
+import * as workspacesApi from "@/lib/api/workspaces";
+
+vi.mock("next/navigation", () => ({
+  useParams: (): { id: string } => ({ id: "ws-test-1" }),
+}));
+
+vi.mock("@/lib/auth/auth-context", () => ({
+  useAuth: (): { user: { id: string } } => ({ user: { id: "u1" } }),
+}));
+
+vi.mock("@/lib/api/workspaces");
+
+vi.mock("@/components/workspace/MemberList", () => ({
+  MemberList: ({ members }: { members: unknown[] }): React.ReactElement => (
+    <div data-testid="member-list">Members: {members.length}</div>
+  ),
+}));
+
+const mockWorkspace = {
+  id: "ws-test-1",
+  name: "Test Workspace",
+  ownerId: "u1",
+  role: "OWNER",
+  createdAt: "2024-01-01",
+};
+
+const mockMembers = [
+  {
+    workspaceId: "ws-test-1",
+    userId: "u1",
+    role: "OWNER",
+    joinedAt: "2024-01-01",
+    user: { id: "u1", email: "a@b.com", name: "Alice", image: null },
+  },
+];
+
+beforeEach(() => {
+  vi.clearAllMocks();
+});
+
+describe("WorkspaceDetailPage", () => {
+  it("loads and renders member list", async (): Promise<void> => {
+    vi.mocked(workspacesApi.fetchUserWorkspaces).mockResolvedValue([mockWorkspace] as never);
+    vi.mocked(workspacesApi.fetchWorkspaceMembers).mockResolvedValue(mockMembers as never);
+    render(<WorkspaceDetailPage />);
+    await waitFor(() => {
+      expect(screen.getByTestId("member-list")).toBeInTheDocument();
+    });
+    expect(screen.getByText("Test Workspace")).toBeInTheDocument();
+  });
+
+  it("shows error state on fetch failure, not member list", async (): Promise<void> => {
+    vi.mocked(workspacesApi.fetchUserWorkspaces).mockRejectedValue(new Error("Network error"));
+    vi.mocked(workspacesApi.fetchWorkspaceMembers).mockRejectedValue(new Error("Network error"));
+    render(<WorkspaceDetailPage />);
+    await waitFor(() => {
+      expect(screen.getByRole("alert")).toBeInTheDocument();
+    });
+    expect(screen.queryByTestId("member-list")).not.toBeInTheDocument();
+  });
+});
diff --git a/apps/web/src/app/(authenticated)/settings/workspaces/[id]/page.tsx b/apps/web/src/app/(authenticated)/settings/workspaces/[id]/page.tsx
index 79dcca8..0104094 100644
--- a/apps/web/src/app/(authenticated)/settings/workspaces/[id]/page.tsx
+++ b/apps/web/src/app/(authenticated)/settings/workspaces/[id]/page.tsx
@@ -1,196 +1,148 @@
 "use client";
 
-import { useState } from "react";
-import { useRouter } from "next/navigation";
-import { WorkspaceSettings } from "@/components/workspace/WorkspaceSettings";
-import { MemberList } from "@/components/workspace/MemberList";
-import { InviteMember } from "@/components/workspace/InviteMember";
-import { WorkspaceMemberRole } from "@mosaic/shared";
-import type { Workspace, WorkspaceMemberWithUser } from "@mosaic/shared";
+import { useCallback, useEffect, useState } from "react";
+import { useParams } from "next/navigation";
 import Link from "next/link";
+import { MemberList } from "@/components/workspace/MemberList";
+import { useAuth } from "@/lib/auth/auth-context";
+import { WorkspaceMemberRole } from "@mosaic/shared";
+import {
+  fetchWorkspaceMembers,
+  fetchUserWorkspaces,
+  updateWorkspaceMemberRole,
+  removeWorkspaceMember,
+  type WorkspaceMemberEntry,
+  type UserWorkspace,
+} from "@/lib/api/workspaces";
+import type { WorkspaceMemberWithUser } from "@/components/workspace/MemberList";
 
-interface WorkspaceDetailPageProps {
-  params: {
-    id: string;
+function getErrorMessage(error: unknown, fallback: string): string {
+  if (error instanceof Error) return error.message;
+  return fallback;
+}
+
+function toMemberWithUser(m: WorkspaceMemberEntry): WorkspaceMemberWithUser {
+  return {
+    workspaceId: m.workspaceId,
+    userId: m.userId,
+    role: m.role,
+    joinedAt: new Date(m.joinedAt),
+    user: {
+      id: m.user.id,
+      email: m.user.email,
+      name: m.user.name ?? "",
+      image: m.user.image,
+      emailVerified: true,
+      authProviderId: null,
+      preferences: {},
+      deactivatedAt: null,
+      isLocalAuth: false,
+      passwordHash: null,
+      invitedBy: null,
+      invitationToken: null,
+      invitedAt: null,
+      createdAt: new Date(),
+      updatedAt: new Date(),
+    },
   };
 }
 
-// Mock data - TODO: Replace with real API calls
-const mockWorkspace: Workspace = {
-  id: "ws-1",
-  name: "Personal Workspace",
-  ownerId: "user-1",
-  settings: {},
-  createdAt: new Date("2024-01-15"),
-  updatedAt: new Date("2024-01-15"),
-};
+export default function WorkspaceDetailPage(): React.ReactElement {
+  const params = useParams<{ id: string }>();
+  const workspaceId = params.id;
+  const { user: authUser } = useAuth();
 
-const mockMembers: WorkspaceMemberWithUser[] = [
-  {
-    workspaceId: "ws-1",
-    userId: "user-1",
-    role: WorkspaceMemberRole.OWNER,
-    joinedAt: new Date("2024-01-15"),
-    user: {
-      id: "user-1",
-      email: "owner@example.com",
-      name: "John Doe",
-      emailVerified: true,
-      image: null,
-      authProviderId: null,
-      preferences: {},
-      deactivatedAt: null,
-      isLocalAuth: false,
-      passwordHash: null,
-      invitedBy: null,
-      invitationToken: null,
-      invitedAt: null,
-      createdAt: new Date("2024-01-15"),
-      updatedAt: new Date("2024-01-15"),
+  const [workspace, setWorkspace] = useState<UserWorkspace | null>(null);
+  const [members, setMembers] = useState<WorkspaceMemberEntry[]>([]);
+  const [isLoading, setIsLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+
+  const load = useCallback(async (): Promise<void> => {
+    setIsLoading(true);
+    setError(null);
+    try {
+      const [workspaces, memberList] = await Promise.all([
+        fetchUserWorkspaces(),
+        fetchWorkspaceMembers(workspaceId),
+      ]);
+      const ws = workspaces.find((w) => w.id === workspaceId) ?? null;
+      setWorkspace(ws);
+      setMembers(memberList);
+    } catch (err) {
+      setError(getErrorMessage(err, "Failed to load workspace"));
+    } finally {
+      setIsLoading(false);
+    }
+  }, [workspaceId]);
+
+  useEffect(() => {
+    void load();
+  }, [load]);
+
+  const handleRoleChange = useCallback(
+    async (userId: string, newRole: WorkspaceMemberRole): Promise<void> => {
+      await updateWorkspaceMemberRole(workspaceId, userId, { role: newRole });
+      await load();
     },
-  },
-  {
-    workspaceId: "ws-1",
-    userId: "user-2",
-    role: WorkspaceMemberRole.ADMIN,
-    joinedAt: new Date("2024-01-16"),
-    user: {
-      id: "user-2",
-      email: "admin@example.com",
-      name: "Jane Smith",
-      emailVerified: true,
-      image: null,
-      authProviderId: null,
-      preferences: {},
-      deactivatedAt: null,
-      isLocalAuth: false,
-      passwordHash: null,
-      invitedBy: null,
-      invitationToken: null,
-      invitedAt: null,
-      createdAt: new Date("2024-01-16"),
-      updatedAt: new Date("2024-01-16"),
+    [workspaceId, load]
+  );
+
+  const handleRemove = useCallback(
+    async (userId: string): Promise<void> => {
+      await removeWorkspaceMember(workspaceId, userId);
+      await load();
     },
-  },
-  {
-    workspaceId: "ws-1",
-    userId: "user-3",
-    role: WorkspaceMemberRole.MEMBER,
-    joinedAt: new Date("2024-01-17"),
-    user: {
-      id: "user-3",
-      email: "member@example.com",
-      name: "Bob Johnson",
-      emailVerified: true,
-      image: null,
-      authProviderId: null,
-      preferences: {},
-      deactivatedAt: null,
-      isLocalAuth: false,
-      passwordHash: null,
-      invitedBy: null,
-      invitationToken: null,
-      invitedAt: null,
-      createdAt: new Date("2024-01-17"),
-      updatedAt: new Date("2024-01-17"),
-    },
-  },
-];
+    [workspaceId, load]
+  );
 
-export default function WorkspaceDetailPage({
-  params,
-}: WorkspaceDetailPageProps): React.JSX.Element {
-  const router = useRouter();
-  const [workspace, setWorkspace] = useState<Workspace>(mockWorkspace);
-  const [members, setMembers] = useState<WorkspaceMemberWithUser[]>(mockMembers);
-  const currentUserId = "user-1"; // TODO: Get from auth context
-  const currentUserRole: WorkspaceMemberRole = WorkspaceMemberRole.OWNER; // TODO: Get from API
-
-  // TODO: Replace with actual role check when API is implemented
-  // Currently hardcoded to OWNER in mock data (line 89)
-  const canInvite =
-    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
-    currentUserRole === WorkspaceMemberRole.OWNER || currentUserRole === WorkspaceMemberRole.ADMIN;
-
-  const handleUpdateWorkspace = async (name: string): Promise<void> => {
-    // TODO: Replace with real API call
-    console.log("Updating workspace:", { id: params.id, name });
-    await new Promise((resolve) => setTimeout(resolve, 500));
-    setWorkspace({ ...workspace, name, updatedAt: new Date() });
-  };
-
-  const handleDeleteWorkspace = async (): Promise<void> => {
-    // TODO: Replace with real API call
-    console.log("Deleting workspace:", params.id);
-    await new Promise((resolve) => setTimeout(resolve, 1000));
-    router.push("/settings/workspaces");
-  };
-
-  const handleRoleChange = async (userId: string, newRole: WorkspaceMemberRole): Promise<void> => {
-    // TODO: Replace with real API call
-    console.log("Changing role:", { userId, newRole });
-    await new Promise((resolve) => setTimeout(resolve, 500));
-    setMembers(
-      members.map((member) => (member.userId === userId ? { ...member, role: newRole } : member))
+  if (isLoading) {
+    return (
+      <div className="p-8 text-center text-gray-500" role="status" aria-label="Loading workspace">
+        Loading workspace…
+      </div>
     );
-  };
+  }
 
-  const handleRemoveMember = async (userId: string): Promise<void> => {
-    // TODO: Replace with real API call
-    console.log("Removing member:", userId);
-    await new Promise((resolve) => setTimeout(resolve, 500));
-    setMembers(members.filter((member) => member.userId !== userId));
-  };
+  if (error) {
+    return (
+      <div className="p-8">
+        <div className="rounded-lg border border-red-200 bg-red-50 p-4 text-red-700" role="alert">
+          <p className="font-medium">Failed to load workspace</p>
+          <p className="mt-1 text-sm">Please try again later.</p>
+        </div>
+        <Link
+          href="/settings/workspaces"
+          className="mt-4 inline-block text-sm text-blue-600 hover:underline"
+        >
+          ← Back to Workspaces
+        </Link>
+      </div>
+    );
+  }
 
-  const handleInviteMember = async (email: string, role: WorkspaceMemberRole): Promise<void> => {
-    // TODO: Replace with real API call
-    console.log("Inviting member:", { email, role, workspaceId: params.id });
-    await new Promise((resolve) => setTimeout(resolve, 1000));
-    // In real implementation, this would send an invitation email
-  };
+  const currentUserId = authUser?.id ?? "";
+  const currentMember = members.find((m) => m.userId === currentUserId);
+  const currentUserRole = currentMember?.role ?? workspace?.role ?? WorkspaceMemberRole.MEMBER;
+  const ownerId =
+    members.find((m) => m.role === WorkspaceMemberRole.OWNER)?.userId ?? workspace?.ownerId ?? "";
 
   return (
-    <main className="container mx-auto px-4 py-8 max-w-5xl">
-      <div className="mb-8">
-        <div className="flex items-center justify-between mb-2">
-          <h1 className="text-3xl font-bold text-gray-900">{workspace.name}</h1>
-          <Link href="/settings/workspaces" className="text-sm text-blue-600 hover:text-blue-700">
-            ← Back to Workspaces
-          </Link>
-        </div>
-        <p className="text-gray-600">Manage workspace settings and team members</p>
+    <div className="p-8 max-w-3xl">
+      <div className="mb-6">
+        <Link href="/settings/workspaces" className="text-sm text-gray-500 hover:text-gray-700">
+          ← Back to Workspaces
+        </Link>
+        <h1 className="mt-2 text-2xl font-bold text-gray-900">{workspace?.name ?? "Workspace"}</h1>
       </div>
 
-      <div className="space-y-6">
-        {/* Workspace Settings */}
-        <WorkspaceSettings
-          workspace={workspace}
-          userRole={currentUserRole}
-          onUpdate={handleUpdateWorkspace}
-          onDelete={handleDeleteWorkspace}
-        />
-
-        {/* Members Section */}
-        <div className="grid grid-cols-1 lg:grid-cols-2 gap-6">
-          <div className="lg:col-span-2">
-            <MemberList
-              members={members}
-              currentUserId={currentUserId}
-              currentUserRole={currentUserRole}
-              workspaceOwnerId={workspace.ownerId}
-              onRoleChange={handleRoleChange}
-              onRemove={handleRemoveMember}
-            />
-          </div>
-
-          {/* Invite Member */}
-          {canInvite && (
-            <div className="lg:col-span-2">
-              <InviteMember onInvite={handleInviteMember} />
-            </div>
-          )}
-        </div>
-      </div>
-    </main>
+      <MemberList
+        members={members.map(toMemberWithUser)}
+        currentUserId={currentUserId}
+        currentUserRole={currentUserRole}
+        workspaceOwnerId={ownerId}
+        onRoleChange={handleRoleChange}
+        onRemove={handleRemove}
+      />
+    </div>
   );
 }
diff --git a/apps/web/src/lib/api/workspaces.ts b/apps/web/src/lib/api/workspaces.ts
index 02fcd33..724e004 100644
--- a/apps/web/src/lib/api/workspaces.ts
+++ b/apps/web/src/lib/api/workspaces.ts
@@ -4,12 +4,8 @@
  */
 
 import type { WorkspaceMemberRole } from "@mosaic/shared";
-import { apiGet, apiPost } from "./client";
+import { apiDelete, apiGet, apiPatch, apiPost } from "./client";
 
-/**
- * A workspace entry from the user's membership list.
- * Matches WorkspaceResponseDto from the API.
- */
 export interface UserWorkspace {
   id: string;
   name: string;
@@ -32,17 +28,57 @@ export interface CreatedWorkspace {
   memberCount: number;
 }
 
-/**
- * Fetch all workspaces the authenticated user is a member of.
- * The API auto-provisions a default workspace if the user has none.
- */
+export interface WorkspaceMemberUser {
+  id: string;
+  email: string;
+  name: string | null;
+  image: string | null;
+}
+
+export interface WorkspaceMemberEntry {
+  workspaceId: string;
+  userId: string;
+  role: WorkspaceMemberRole;
+  joinedAt: string;
+  user: WorkspaceMemberUser;
+}
+
+export interface AddMemberDto {
+  userId: string;
+  role: WorkspaceMemberRole;
+}
+
+export interface UpdateMemberRoleDto {
+  role: WorkspaceMemberRole;
+}
+
 export async function fetchUserWorkspaces(): Promise<UserWorkspace[]> {
   return apiGet<UserWorkspace[]>("/api/workspaces");
 }
 
-/**
- * Create a workspace through the admin endpoint.
- */
 export async function createWorkspace(dto: CreateWorkspaceDto): Promise<CreatedWorkspace> {
   return apiPost<CreatedWorkspace>("/api/admin/workspaces", dto);
 }
+
+export async function fetchWorkspaceMembers(workspaceId: string): Promise<WorkspaceMemberEntry[]> {
+  return apiGet<WorkspaceMemberEntry[]>(`/api/workspaces/${workspaceId}/members`);
+}
+
+export async function addWorkspaceMember(
+  workspaceId: string,
+  dto: AddMemberDto
+): Promise<WorkspaceMemberEntry> {
+  return apiPost<WorkspaceMemberEntry>(`/api/workspaces/${workspaceId}/members`, dto);
+}
+
+export async function updateWorkspaceMemberRole(
+  workspaceId: string,
+  userId: string,
+  dto: UpdateMemberRoleDto
+): Promise<WorkspaceMemberEntry> {
+  return apiPatch<WorkspaceMemberEntry>(`/api/workspaces/${workspaceId}/members/${userId}`, dto);
+}
+
+export async function removeWorkspaceMember(workspaceId: string, userId: string): Promise<void> {
+  await apiDelete<unknown>(`/api/workspaces/${workspaceId}/members/${userId}`);
+}