diff --git a/src/app/(staff)/staff/clients/add/page.tsx b/src/app/(staff)/staff/clients/add/page.tsx
new file mode 100644
index 0000000..4e6e59d
--- /dev/null
+++ b/src/app/(staff)/staff/clients/add/page.tsx
@@ -0,0 +1,22 @@
+import type { Metadata } from "next";
+import { redirect } from "next/navigation";
+import { TopNav } from "@/components/navigation/top-nav";
+import { getActingBusinessContext } from "@/lib/business/get-acting-business-context";
+import { AddClientForm } from "@/features/staff/components/add-client-form";
+
+export const metadata: Metadata = { title: "Add Client" };
+export const dynamic = "force-dynamic";
+
+export default async function AddClientPage() {
+  const context = await getActingBusinessContext();
+  if (!context) redirect("/home");
+
+  return (
+    <div className="pb-12">
+      <TopNav title="Add Client" onBack sticky className="bg-stone" />
+      <main className="mx-auto max-w-2xl px-6 py-6">
+        <AddClientForm />
+      </main>
+    </div>
+  );
+}
diff --git a/src/app/(staff)/staff/clients/page.tsx b/src/app/(staff)/staff/clients/page.tsx
index 8a2005d..11a214c 100644
--- a/src/app/(staff)/staff/clients/page.tsx
+++ b/src/app/(staff)/staff/clients/page.tsx
@@ -1,5 +1,5 @@
 import type { Metadata } from "next";
-import { Search, Users } from "lucide-react";
+import { Plus, Search, Users } from "lucide-react";
 import Link from "next/link";
 import { redirect } from "next/navigation";
 import { EmptyState } from "@/components/feedback/empty-state";
@@ -78,6 +78,15 @@ export default async function StaffClientsPage({
         sticky
         className="bg-stone"
         leftAction={<InlineNotificationBell href="/staff/notifications" unreadCount={unreadNotificationCount} />}
+        action={
+          <Link
+            href="/staff/clients/add"
+            className="bg-ink flex h-10 w-10 items-center justify-center rounded-full text-white"
+            aria-label="Add client"
+          >
+            <Plus className="h-4 w-4" aria-hidden="true" />
+          </Link>
+        }
       />
 
       <div className="px-6 pt-6">
diff --git a/src/features/staff/actions/clients.ts b/src/features/staff/actions/clients.ts
new file mode 100644
index 0000000..cb7eebd
--- /dev/null
+++ b/src/features/staff/actions/clients.ts
@@ -0,0 +1,56 @@
+"use server";
+
+import { revalidatePath } from "next/cache";
+import { registerRequestSchema } from "@/features/auth/schemas";
+import { getActingBusinessContext } from "@/lib/business/get-acting-business-context";
+import { writeAuditLog } from "@/lib/audit/write-audit-log";
+import { prisma } from "@/lib/db/prisma";
+import { createCustomerByStaff } from "@/services/customer/customer.service";
+
+export interface AddClientInput {
+  firstName: string;
+  lastName: string;
+  email: string;
+  phone?: string;
+}
+
+export interface AddClientResult {
+  success: boolean;
+  error?: string;
+  customerId?: string;
+}
+
+/**
+ * Open to any signed-in staff/owner/super-admin — the same gate the
+ * Clients page itself uses (see (staff)/staff/clients/page.tsx), not
+ * owner-only: a walk-in's details are just as often taken by whoever's
+ * on the floor as by the owner.
+ */
+export async function addClientAction(input: AddClientInput): Promise<AddClientResult> {
+  const context = await getActingBusinessContext();
+  if (!context) return { success: false, error: "You must be signed in as staff." };
+
+  const parsed = registerRequestSchema.safeParse(input);
+  if (!parsed.success) {
+    return { success: false, error: parsed.error.issues[0]?.message ?? "Please check the form." };
+  }
+
+  const result = await createCustomerByStaff(prisma, parsed.data);
+  if (!result.success) return result;
+
+  await writeAuditLog(prisma, {
+    actorUserId: context.userId,
+    action: "CUSTOMER_ADDED_BY_STAFF",
+    entityType: "CustomerProfile",
+    entityId: result.customerId!,
+    metadata: { email: parsed.data.email },
+  });
+
+  // The new client won't actually show up in the Clients list until they
+  // have an appointment (see that page's own "belongs to this business is
+  // via the appointment relation" note) — revalidated anyway so the list
+  // is fresh the moment that happens, without a stale cache lingering.
+  revalidatePath("/staff/clients");
+
+  return result;
+}
diff --git a/src/features/staff/components/add-client-form.tsx b/src/features/staff/components/add-client-form.tsx
new file mode 100644
index 0000000..28ab352
--- /dev/null
+++ b/src/features/staff/components/add-client-form.tsx
@@ -0,0 +1,85 @@
+"use client";
+
+import Link from "next/link";
+import { useRouter } from "next/navigation";
+import { useState, useTransition } from "react";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { addClientAction } from "../actions/clients";
+
+/**
+ * A walk-in's details taken over the counter — creates a real account
+ * (see createCustomerByStaff) rather than a guest profile, so the
+ * customer can sign in later with just their email, no password. They're
+ * never emailed anything about this; the app only reaches out once they
+ * ask to sign in themselves.
+ */
+export function AddClientForm() {
+  const router = useRouter();
+  const [firstName, setFirstName] = useState("");
+  const [lastName, setLastName] = useState("");
+  const [email, setEmail] = useState("");
+  const [phone, setPhone] = useState("");
+  const [error, setError] = useState<string | null>(null);
+  const [added, setAdded] = useState<{ customerId: string; name: string } | null>(null);
+  const [isPending, startTransition] = useTransition();
+
+  const submit = () => {
+    setError(null);
+    startTransition(async () => {
+      const result = await addClientAction({ firstName, lastName, email, phone: phone || undefined });
+      if (!result.success || !result.customerId) {
+        setError(result.error ?? "Couldn't add this client.");
+        return;
+      }
+      setAdded({ customerId: result.customerId, name: `${firstName} ${lastName}`.trim() });
+    });
+  };
+
+  if (added) {
+    return (
+      <div className="space-y-4 rounded-md border-line border bg-white p-6">
+        <p className="text-sm font-bold">{added.name} has been added.</p>
+        <p className="text-muted text-sm">
+          They can sign in anytime with just their email — no password, no invite email sent. They&apos;ll show up
+          in Clients once they have an appointment.
+        </p>
+        <div className="flex gap-3">
+          <Button variant="secondary" className="flex-1" onClick={() => router.push("/staff/clients")}>
+            Done
+          </Button>
+          <Button asChild className="flex-1">
+            <Link href={`/staff/book?customerId=${added.customerId}`}>Book Appointment</Link>
+          </Button>
+        </div>
+      </div>
+    );
+  }
+
+  return (
+    <div className="space-y-4">
+      <div className="rounded-md border-line space-y-4 border bg-white p-6">
+        <div className="grid grid-cols-2 gap-3">
+          <Input label="First Name" required value={firstName} onChange={(e) => setFirstName(e.target.value)} />
+          <Input label="Last Name" required value={lastName} onChange={(e) => setLastName(e.target.value)} />
+        </div>
+        <Input label="Email" type="email" required value={email} onChange={(e) => setEmail(e.target.value)} />
+        <Input label="Phone (optional)" type="tel" value={phone} onChange={(e) => setPhone(e.target.value)} />
+      </div>
+
+      {error && (
+        <p role="alert" className="text-danger text-sm font-medium">
+          {error}
+        </p>
+      )}
+      <Button
+        className="w-full"
+        isLoading={isPending}
+        disabled={!firstName.trim() || !lastName.trim() || !email.trim()}
+        onClick={submit}
+      >
+        Add Client
+      </Button>
+    </div>
+  );
+}
diff --git a/src/services/customer/__tests__/customer.service.integration.test.ts b/src/services/customer/__tests__/customer.service.integration.test.ts
index 2f6fb08..4827969 100644
--- a/src/services/customer/__tests__/customer.service.integration.test.ts
+++ b/src/services/customer/__tests__/customer.service.integration.test.ts
@@ -1,5 +1,5 @@
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
-import { setCustomerAvatar, updateCustomerProfile, updatePreferredBarber } from "@/services/customer/customer.service";
+import { createCustomerByStaff, setCustomerAvatar, updateCustomerProfile, updatePreferredBarber } from "@/services/customer/customer.service";
 import {
   cleanupTestBusiness,
   createTestBusiness,
@@ -141,4 +141,54 @@ describe("customer.service (integration)", () => {
       expect(result.success).toBe(false);
     });
   });
+
+  describe("createCustomerByStaff", () => {
+    async function trackForCleanup(customerId: string) {
+      const profile = await prisma.customerProfile.findUniqueOrThrow({ where: { id: customerId } });
+      business.createdUserIds.push(profile.userId!);
+    }
+
+    it("creates a registered (non-guest) account with emailVerified already set", async () => {
+      const email = `walkin-${Date.now()}@test.local`;
+      const result = await createCustomerByStaff(prisma, { firstName: "Alex", lastName: "Kim", email, phone: "+44 7700 900123" });
+      expect(result.success).toBe(true);
+      await trackForCleanup(result.customerId!);
+
+      const profile = await prisma.customerProfile.findUniqueOrThrow({ where: { id: result.customerId } });
+      expect(profile.firstName).toBe("Alex");
+      expect(profile.lastName).toBe("Kim");
+      expect(profile.email).toBe(email);
+      expect(profile.phone).toBe("+44 7700 900123");
+      expect(profile.isGuest).toBe(false);
+      expect(profile.userId).toBeTruthy();
+
+      const user = await prisma.user.findUniqueOrThrow({ where: { id: profile.userId! } });
+      expect(user.email).toBe(email);
+      // Must be set, not null — requestOtp's onlyIfUserExists (see
+      // otp.service.ts) refuses to ever send a login code otherwise,
+      // which would silently and permanently lock this customer out.
+      expect(user.emailVerified).not.toBeNull();
+    });
+
+    it("lowercases and trims the email, and normalizes a blank phone to null", async () => {
+      const email = `  Walkin-${Date.now()}@Test.local  `;
+      const result = await createCustomerByStaff(prisma, { firstName: " Alex ", lastName: " Kim ", email, phone: "" });
+      expect(result.success).toBe(true);
+      await trackForCleanup(result.customerId!);
+
+      const profile = await prisma.customerProfile.findUniqueOrThrow({ where: { id: result.customerId } });
+      expect(profile.email).toBe(email.trim().toLowerCase());
+      expect(profile.firstName).toBe("Alex");
+      expect(profile.phone).toBeNull();
+    });
+
+    it("rejects an email already in use by another account", async () => {
+      const { userId } = await createTestCustomer(business);
+      const existingUser = await prisma.user.findUniqueOrThrow({ where: { id: userId } });
+
+      const result = await createCustomerByStaff(prisma, { firstName: "Alex", lastName: "Kim", email: existingUser.email! });
+      expect(result.success).toBe(false);
+      expect(result.error).toMatch(/already exists/i);
+    });
+  });
 });
diff --git a/src/services/customer/customer.service.ts b/src/services/customer/customer.service.ts
index 46ca166..ee8cdcd 100644
--- a/src/services/customer/customer.service.ts
+++ b/src/services/customer/customer.service.ts
@@ -125,6 +125,69 @@ async function resolveGuestCustomer(
   return { customerId: created.id, isNewProfile: true };
 }
 
+export interface CreateCustomerByStaffParams {
+  firstName: string;
+  lastName: string;
+  email: string;
+  phone?: string;
+}
+
+export interface CreateCustomerByStaffResult {
+  success: boolean;
+  error?: string;
+  customerId?: string;
+}
+
+/**
+ * A staff/owner member adding a client who isn't self-registering right
+ * now — e.g. a walk-in's details taken over the counter (see
+ * features/staff/actions/clients.ts, the only caller). Produces the exact
+ * same shape a real self-service registration does (register.ts) —
+ * `isGuest: false`, `emailVerified` already set — specifically so the
+ * customer can sign in immediately afterward on the normal sign-in page.
+ * requestOtp's `onlyIfUserExists` check (see otp.service.ts) refuses to
+ * ever send a login code for a User whose `emailVerified` isn't set, so
+ * leaving that null here would silently and permanently lock them out —
+ * not a partial/pending account the way a staff invitation is.
+ *
+ * Deliberately does not call notify()/requestOtp() at all — the customer
+ * hears nothing until they themselves ask to sign in later. Does not
+ * attempt to match/attach an existing guest CustomerProfile with the same
+ * email/phone either — full guest-to-registered account claiming is an
+ * explicit out-of-scope case for this service (see this file's own
+ * header); a plain email-uniqueness check against User is enough here,
+ * same as register.ts.
+ */
+export async function createCustomerByStaff(
+  prisma: PrismaClient,
+  params: CreateCustomerByStaffParams,
+): Promise<CreateCustomerByStaffResult> {
+  const email = params.email.trim().toLowerCase();
+  const firstName = params.firstName.trim();
+  const lastName = params.lastName.trim();
+  const phone = params.phone?.trim() || null;
+
+  const existing = await prisma.user.findUnique({ where: { email }, select: { id: true } });
+  if (existing) {
+    return { success: false, error: "A customer with this email already exists." };
+  }
+
+  const user = await prisma.user.create({
+    data: {
+      email,
+      phone,
+      name: `${firstName} ${lastName}`.trim(),
+      emailVerified: new Date(),
+      customerProfile: {
+        create: { firstName, lastName, email, phone, isGuest: false },
+      },
+    },
+    include: { customerProfile: true },
+  });
+
+  return { success: true, customerId: user.customerProfile!.id };
+}
+
 /**
  * Staff-directory search (src/app/(staff)/staff/clients). Deliberately a
  * plain in-memory filter, not a Prisma `contains`/`mode: "insensitive"`