diff --git a/src/organizer/dto/lookup-user.dto.ts b/src/organizer/dto/lookup-user.dto.ts
new file mode 100644
index 0000000..81b19e5
--- /dev/null
+++ b/src/organizer/dto/lookup-user.dto.ts
@@ -0,0 +1,21 @@
+import { IsEmail, IsOptional, IsString, MinLength } from 'class-validator';
+
+/**
+ * Query for `GET /organizer/users/lookup`, used by the mobile Check-in
+ * team screen to resolve a teammate before granting ticket-admin.
+ *
+ * Provide exactly one of:
+ *  - `email` — exact, case-insensitive match → a single user (or 404).
+ *  - `q` — prefix/substring across email + name → up to 10 users, for
+ *    type-ahead. Min length guards against broad enumeration.
+ */
+export class LookupUserDto {
+  @IsOptional()
+  @IsEmail()
+  email?: string;
+
+  @IsOptional()
+  @IsString()
+  @MinLength(2)
+  q?: string;
+}
diff --git a/src/organizer/organizer.controller.ts b/src/organizer/organizer.controller.ts
index ce71182..9a0c58c 100644
--- a/src/organizer/organizer.controller.ts
+++ b/src/organizer/organizer.controller.ts
@@ -21,6 +21,7 @@ import { Roles } from '../common/decorators/roles.decorator';
 import { SkipTransform } from '../common/decorators/skip-transform.decorator';
 import { EnableMonnifyDto } from './dto/enable-monnify.dto';
 import { EnablePaystackDto } from './dto/enable-paystack.dto';
+import { LookupUserDto } from './dto/lookup-user.dto';
 import { QueryOrganizerEventsDto } from './dto/query-organizer-events.dto';
 import { QueryAttendeesDto } from './dto/query-attendees.dto';
 import { QueryPayoutsDto } from './dto/query-payouts.dto';
@@ -122,6 +123,15 @@ export class OrganizerController {
     return this.organizer.updateBankDetails(userId, dto);
   }
 
+  @Get('users/lookup')
+  @Roles(UserRole.ORGANIZER)
+  @ApiOperation({
+    summary: 'Resolve a teammate by email (or prefix) for the check-in team',
+  })
+  lookupUsers(@Query() query: LookupUserDto) {
+    return this.organizer.lookupUsers(query);
+  }
+
   @Get('events/:id/ticket-admins')
   @Roles(UserRole.ORGANIZER)
   @ApiOperation({ summary: 'List active check-in delegates (ticket admins)' })
diff --git a/src/organizer/organizer.service.spec.ts b/src/organizer/organizer.service.spec.ts
index 4d12e6c..4e4f070 100644
--- a/src/organizer/organizer.service.spec.ts
+++ b/src/organizer/organizer.service.spec.ts
@@ -700,3 +700,77 @@ describe('OrganizerService.updateBankDetails', () => {
     expect(res.bankName).toBe('Old Bank');
   });
 });
+
+describe('OrganizerService.lookupUsers', () => {
+  function lookupSvc(opts: { found?: unknown; list?: unknown[] } = {}) {
+    const findFirst = jest.fn().mockResolvedValue(
+      opts.found === undefined
+        ? {
+            id: 'u-1',
+            firstName: 'Jane',
+            lastName: 'Doe',
+            email: 'jane@x.com',
+          }
+        : opts.found,
+    );
+    const findMany = jest.fn().mockResolvedValue(opts.list ?? []);
+    const prisma = {
+      user: { findFirst, findMany },
+    } as unknown as PrismaService;
+
+    const svc = new OrganizerService(
+      prisma,
+      { get: () => undefined } as unknown as ConfigService,
+      {} as unknown as PaystackService,
+      {} as unknown as MonnifyProvider,
+    );
+    return { svc, findFirst, findMany };
+  }
+
+  it('resolves an exact email (case-insensitive, trimmed) to id/name/email', async () => {
+    const { svc, findFirst } = lookupSvc();
+
+    const res = await svc.lookupUsers({ email: '  Jane@X.com ' });
+
+    expect(findFirst).toHaveBeenCalledWith(
+      expect.objectContaining({
+        where: { email: { equals: 'Jane@X.com', mode: 'insensitive' } },
+      }),
+    );
+    expect(res).toEqual({ id: 'u-1', name: 'Jane Doe', email: 'jane@x.com' });
+  });
+
+  it('404s when no user has that email', async () => {
+    const { svc } = lookupSvc({ found: null });
+    await expect(
+      svc.lookupUsers({ email: 'nobody@x.com' }),
+    ).rejects.toBeInstanceOf(NotFoundException);
+  });
+
+  it('returns a capped list for a prefix query', async () => {
+    const { svc, findMany } = lookupSvc({
+      list: [
+        {
+          id: 'u-2',
+          firstName: 'Jan',
+          lastName: 'Kowalski',
+          email: 'jan@x.com',
+        },
+      ],
+    });
+
+    const res = await svc.lookupUsers({ q: 'jan' });
+
+    expect(findMany).toHaveBeenCalledWith(
+      expect.objectContaining({ take: 10 }),
+    );
+    expect(res).toEqual([
+      { id: 'u-2', name: 'Jan Kowalski', email: 'jan@x.com' },
+    ]);
+  });
+
+  it('rejects when neither email nor q is provided', async () => {
+    const { svc } = lookupSvc();
+    await expect(svc.lookupUsers({})).rejects.toThrow(/email or q/);
+  });
+});
diff --git a/src/organizer/organizer.service.ts b/src/organizer/organizer.service.ts
index 403ccd1..7425ba3 100644
--- a/src/organizer/organizer.service.ts
+++ b/src/organizer/organizer.service.ts
@@ -20,6 +20,7 @@ import { PaystackService } from '../paystack/paystack.service';
 import { PrismaService } from '../prisma/prisma.service';
 import { EnableMonnifyDto } from './dto/enable-monnify.dto';
 import { EnablePaystackDto } from './dto/enable-paystack.dto';
+import { LookupUserDto } from './dto/lookup-user.dto';
 import { QueryOrganizerEventsDto } from './dto/query-organizer-events.dto';
 import { QueryAttendeesDto } from './dto/query-attendees.dto';
 import { UpdateBankDetailsDto } from './dto/update-bank-details.dto';
@@ -85,6 +86,63 @@ export class OrganizerService {
     private readonly monnify: MonnifyProvider,
   ) {}
 
+  /**
+   * Resolve a teammate for the Check-in team screen (#101). Feeds
+   * `POST /organizer/events/:id/ticket-admins`, which takes userIds —
+   * organizers only know a teammate's email.
+   *
+   * With `email`: exact, case-insensitive, trimmed match → the single
+   * user (404 if none). With `q`: a small prefix/substring list across
+   * email + name for type-ahead. Returns only id/name/email — no
+   * wallets, phone, or role.
+   */
+  async lookupUsers(dto: LookupUserDto) {
+    const email = dto.email?.trim();
+    const q = dto.q?.trim();
+
+    if (email) {
+      const user = await this.prisma.user.findFirst({
+        where: { email: { equals: email, mode: 'insensitive' } },
+        select: { id: true, firstName: true, lastName: true, email: true },
+      });
+      if (!user) {
+        throw new NotFoundException('No HostIT account for that email');
+      }
+      return this.toLookupDto(user);
+    }
+
+    if (q) {
+      const users = await this.prisma.user.findMany({
+        where: {
+          OR: [
+            { email: { contains: q, mode: 'insensitive' } },
+            { firstName: { contains: q, mode: 'insensitive' } },
+            { lastName: { contains: q, mode: 'insensitive' } },
+          ],
+        },
+        select: { id: true, firstName: true, lastName: true, email: true },
+        orderBy: { email: 'asc' },
+        take: 10,
+      });
+      return users.map((u) => this.toLookupDto(u));
+    }
+
+    throw new BadRequestException('Provide an email or q query parameter');
+  }
+
+  private toLookupDto(u: {
+    id: string;
+    firstName: string;
+    lastName: string;
+    email: string;
+  }) {
+    return {
+      id: u.id,
+      name: `${u.firstName} ${u.lastName}`.trim(),
+      email: u.email,
+    };
+  }
+
   /**
    * Organizer dashboard landing: the caller's events with per-event and
    * per-ticket-type sales stats, plus a top-level summary computed across