diff --git a/packages/twenty-front/src/modules/auth/sign-in-up/hooks/useSignInUp.tsx b/packages/twenty-front/src/modules/auth/sign-in-up/hooks/useSignInUp.tsx
index 142b78813..506001e38 100644
--- a/packages/twenty-front/src/modules/auth/sign-in-up/hooks/useSignInUp.tsx
+++ b/packages/twenty-front/src/modules/auth/sign-in-up/hooks/useSignInUp.tsx
@@ -72,14 +72,24 @@ export const useSignInUp = (form: UseFormReturn<Form>) => {
       },
       onCompleted: (data) => {
         if (data?.checkUserExists.exists) {
-          setSignInUpMode(SignInUpMode.SignIn);
+          isMatchingLocation(AppPath.Invite)
+            ? setSignInUpMode(SignInUpMode.Invite)
+            : setSignInUpMode(SignInUpMode.SignIn);
         } else {
-          setSignInUpMode(SignInUpMode.SignUp);
+          isMatchingLocation(AppPath.Invite)
+            ? setSignInUpMode(SignInUpMode.Invite)
+            : setSignInUpMode(SignInUpMode.SignUp);
         }
         setSignInUpStep(SignInUpStep.Password);
       },
     });
-  }, [setSignInUpStep, checkUserExistsQuery, form, setSignInUpMode]);
+  }, [
+    isMatchingLocation,
+    setSignInUpStep,
+    checkUserExistsQuery,
+    form,
+    setSignInUpMode,
+  ]);
 
   const submitCredentials: SubmitHandler<Form> = useCallback(
     async (data) => {
diff --git a/packages/twenty-server/src/core/auth/auth.module.ts b/packages/twenty-server/src/core/auth/auth.module.ts
index adcc31f7f..fe40a5c39 100644
--- a/packages/twenty-server/src/core/auth/auth.module.ts
+++ b/packages/twenty-server/src/core/auth/auth.module.ts
@@ -18,6 +18,7 @@ import { GoogleGmailAuthController } from 'src/core/auth/controllers/google-gmai
 import { VerifyAuthController } from 'src/core/auth/controllers/verify-auth.controller';
 import { TokenService } from 'src/core/auth/services/token.service';
 import { GoogleGmailService } from 'src/core/auth/services/google-gmail.service';
+import { UserWorkspaceModule } from 'src/core/user-workspace/user-workspace.module';
 
 import { AuthResolver } from './auth.resolver';
 
@@ -45,6 +46,7 @@ const jwtModule = JwtModule.registerAsync({
     TypeORMModule,
     TypeOrmModule.forFeature([Workspace, User, RefreshToken], 'core'),
     HttpModule,
+    UserWorkspaceModule,
   ],
   controllers: [
     GoogleAuthController,
diff --git a/packages/twenty-server/src/core/auth/auth.resolver.ts b/packages/twenty-server/src/core/auth/auth.resolver.ts
index c2b2b2cea..686fcee98 100644
--- a/packages/twenty-server/src/core/auth/auth.resolver.ts
+++ b/packages/twenty-server/src/core/auth/auth.resolver.ts
@@ -91,6 +91,7 @@ export class AuthResolver {
   @Mutation(() => LoginToken)
   async signUp(@Args() signUpInput: SignUpInput): Promise<LoginToken> {
     const user = await this.authService.signUp(signUpInput);
+
     const loginToken = await this.tokenService.generateLoginToken(user.email);
 
     return { loginToken };
@@ -120,6 +121,8 @@ export class AuthResolver {
       verifyInput.loginToken,
     );
 
+    assert(email, 'Invalid token', ForbiddenException);
+
     const result = await this.authService.verify(email);
 
     return result;
diff --git a/packages/twenty-server/src/core/auth/services/auth.service.spec.ts b/packages/twenty-server/src/core/auth/services/auth.service.spec.ts
index 5776705a0..21e498657 100644
--- a/packages/twenty-server/src/core/auth/services/auth.service.spec.ts
+++ b/packages/twenty-server/src/core/auth/services/auth.service.spec.ts
@@ -9,6 +9,7 @@ import { Workspace } from 'src/core/workspace/workspace.entity';
 import { User } from 'src/core/user/user.entity';
 import { EnvironmentService } from 'src/integrations/environment/environment.service';
 import { EmailService } from 'src/integrations/email/email.service';
+import { UserWorkspaceService } from 'src/core/user-workspace/user-workspace.service';
 
 import { AuthService } from './auth.service';
 import { TokenService } from './token.service';
@@ -28,6 +29,10 @@ describe('AuthService', () => {
           provide: UserService,
           useValue: {},
         },
+        {
+          provide: UserWorkspaceService,
+          useValue: {},
+        },
         {
           provide: WorkspaceManagerService,
           useValue: {},
diff --git a/packages/twenty-server/src/core/auth/services/auth.service.ts b/packages/twenty-server/src/core/auth/services/auth.service.ts
index 2b481a836..990200711 100644
--- a/packages/twenty-server/src/core/auth/services/auth.service.ts
+++ b/packages/twenty-server/src/core/auth/services/auth.service.ts
@@ -34,6 +34,7 @@ import { EnvironmentService } from 'src/integrations/environment/environment.ser
 import { EmailService } from 'src/integrations/email/email.service';
 import { UpdatePassword } from 'src/core/auth/dto/update-password.entity';
 import { getImageBufferFromUrl } from 'src/utils/image';
+import { UserWorkspaceService } from 'src/core/user-workspace/user-workspace.service';
 
 import { TokenService } from './token.service';
 
@@ -54,6 +55,7 @@ export class AuthService {
     private readonly workspaceRepository: Repository<Workspace>,
     @InjectRepository(User, 'core')
     private readonly userRepository: Repository<User>,
+    private readonly userWorkspaceService: UserWorkspaceService,
     private readonly httpService: HttpService,
     private readonly environmentService: EnvironmentService,
     private readonly emailService: EmailService,
@@ -95,11 +97,16 @@ export class AuthService {
     if (!firstName) firstName = '';
     if (!lastName) lastName = '';
 
-    const existingUser = await this.userRepository.findOneBy({
-      email: email,
+    const existingUser = await this.userRepository.findOne({
+      where: {
+        email: email,
+      },
+      relations: ['defaultWorkspace'],
     });
 
-    assert(!existingUser, 'This user already exists', ForbiddenException);
+    if (existingUser && !workspaceInviteHash) {
+      assert(!existingUser, 'This user already exists', ForbiddenException);
+    }
 
     if (password) {
       const isPasswordValid = PASSWORD_REGEX.test(password);
@@ -157,6 +164,31 @@ export class AuthService {
       imagePath = paths[0];
     }
 
+    if (existingUser && workspaceInviteHash) {
+      const userWorkspaceExists =
+        await this.userWorkspaceService.checkUserWorkspaceExists(
+          existingUser.id,
+          workspace.id,
+        );
+
+      if (!userWorkspaceExists) {
+        await this.userWorkspaceService.create(existingUser.id, workspace.id);
+
+        await this.userWorkspaceService.createWorkspaceMember(
+          workspace.id,
+          existingUser,
+        );
+      }
+
+      const updatedUser = await this.userRepository.save({
+        id: existingUser.id,
+        defaultWorkspace: workspace,
+        updatedAt: new Date().toISOString(),
+      });
+
+      return Object.assign(existingUser, updatedUser);
+    }
+
     const userToCreate = this.userRepository.create({
       email: email,
       firstName: firstName,
@@ -169,9 +201,8 @@ export class AuthService {
 
     const user = await this.userRepository.save(userToCreate);
 
-    if (workspaceInviteHash) {
-      await this.userService.createWorkspaceMember(user);
-    }
+    await this.userWorkspaceService.create(user.id, workspace.id);
+    await this.userWorkspaceService.createWorkspaceMember(workspace.id, user);
 
     return user;
   }
diff --git a/packages/twenty-server/src/core/user-workspace/user-workspace.entity.ts b/packages/twenty-server/src/core/user-workspace/user-workspace.entity.ts
new file mode 100644
index 000000000..adb1e0e06
--- /dev/null
+++ b/packages/twenty-server/src/core/user-workspace/user-workspace.entity.ts
@@ -0,0 +1,48 @@
+import { Field, ID, ObjectType } from '@nestjs/graphql';
+
+import { IDField } from '@ptc-org/nestjs-query-graphql';
+import {
+  Column,
+  CreateDateColumn,
+  Entity,
+  JoinColumn,
+  PrimaryGeneratedColumn,
+  Unique,
+  UpdateDateColumn,
+} from 'typeorm';
+
+import { User } from 'src/core/user/user.entity';
+import { Workspace } from 'src/core/workspace/workspace.entity';
+
+@Entity({ name: 'userWorkspace', schema: 'core' })
+@ObjectType('UserWorkspace')
+@Unique('IndexOnUserIdAndWorkspaceIdUnique', ['userId', 'workspaceId'])
+export class UserWorkspace {
+  @IDField(() => ID)
+  @PrimaryGeneratedColumn('uuid')
+  id: string;
+
+  @JoinColumn({ name: 'userId' })
+  user: User;
+
+  @Column()
+  userId: string;
+
+  @JoinColumn({ name: 'workspaceId' })
+  workspace: Workspace;
+
+  @Column()
+  workspaceId: string;
+
+  @Field()
+  @CreateDateColumn({ type: 'timestamp with time zone' })
+  createdAt: Date;
+
+  @Field()
+  @UpdateDateColumn({ type: 'timestamp with time zone' })
+  updatedAt: Date;
+
+  @Field()
+  @Column('timestamp with time zone')
+  deletedAt: Date;
+}
diff --git a/packages/twenty-server/src/core/user-workspace/user-workspace.module.ts b/packages/twenty-server/src/core/user-workspace/user-workspace.module.ts
new file mode 100644
index 000000000..6ce5ba891
--- /dev/null
+++ b/packages/twenty-server/src/core/user-workspace/user-workspace.module.ts
@@ -0,0 +1,25 @@
+import { Module } from '@nestjs/common';
+
+import { NestjsQueryGraphQLModule } from '@ptc-org/nestjs-query-graphql';
+import { NestjsQueryTypeOrmModule } from '@ptc-org/nestjs-query-typeorm';
+
+import { TypeORMModule } from 'src/database/typeorm/typeorm.module';
+import { UserWorkspace } from 'src/core/user-workspace/user-workspace.entity';
+import { UserWorkspaceService } from 'src/core/user-workspace/user-workspace.service';
+import { DataSourceModule } from 'src/metadata/data-source/data-source.module';
+
+@Module({
+  imports: [
+    NestjsQueryGraphQLModule.forFeature({
+      imports: [
+        NestjsQueryTypeOrmModule.forFeature([UserWorkspace], 'core'),
+        TypeORMModule,
+        DataSourceModule,
+      ],
+      services: [UserWorkspaceService],
+    }),
+  ],
+  exports: [UserWorkspaceService],
+  providers: [UserWorkspaceService],
+})
+export class UserWorkspaceModule {}
diff --git a/packages/twenty-server/src/core/user-workspace/user-workspace.service.ts b/packages/twenty-server/src/core/user-workspace/user-workspace.service.ts
new file mode 100644
index 000000000..bb4d7a83c
--- /dev/null
+++ b/packages/twenty-server/src/core/user-workspace/user-workspace.service.ts
@@ -0,0 +1,65 @@
+import { InjectRepository } from '@nestjs/typeorm';
+
+import { TypeOrmQueryService } from '@ptc-org/nestjs-query-typeorm';
+import { Repository } from 'typeorm';
+
+import { UserWorkspace } from 'src/core/user-workspace/user-workspace.entity';
+import { TypeORMService } from 'src/database/typeorm/typeorm.service';
+import { DataSourceService } from 'src/metadata/data-source/data-source.service';
+import { User } from 'src/core/user/user.entity';
+
+export class UserWorkspaceService extends TypeOrmQueryService<UserWorkspace> {
+  constructor(
+    @InjectRepository(UserWorkspace, 'core')
+    private readonly userWorkspaceRepository: Repository<UserWorkspace>,
+    private readonly dataSourceService: DataSourceService,
+    private readonly typeORMService: TypeORMService,
+  ) {
+    super(userWorkspaceRepository);
+  }
+
+  async create(userId: string, workspaceId: string): Promise<UserWorkspace> {
+    const userWorkspace = this.userWorkspaceRepository.create({
+      userId,
+      workspaceId,
+    });
+
+    return this.userWorkspaceRepository.save(userWorkspace);
+  }
+
+  async createWorkspaceMember(workspaceId: string, user: User) {
+    const dataSourceMetadata =
+      await this.dataSourceService.getLastDataSourceMetadataFromWorkspaceIdOrFail(
+        workspaceId,
+      );
+
+    const workspaceDataSource =
+      await this.typeORMService.connectToDataSource(dataSourceMetadata);
+
+    await workspaceDataSource?.query(
+      `INSERT INTO ${dataSourceMetadata.schema}."workspaceMember"
+        ("nameFirstName", "nameLastName", "colorScheme", "userId", "userEmail", "avatarUrl")
+        VALUES ('${user.firstName}', '${user.lastName}', 'Light', '${
+          user.id
+        }', '${user.email}', '${user.defaultAvatarUrl ?? ''}')`,
+    );
+  }
+
+  async findUserWorkspaces(userId: string): Promise<UserWorkspace[]> {
+    return this.userWorkspaceRepository.find({
+      where: {
+        userId,
+      },
+    });
+  }
+
+  async checkUserWorkspaceExists(
+    userId: string,
+    workspaceId: string,
+  ): Promise<UserWorkspace | null> {
+    return this.userWorkspaceRepository.findOneBy({
+      userId,
+      workspaceId,
+    });
+  }
+}
diff --git a/packages/twenty-server/src/core/user/services/user.service.ts b/packages/twenty-server/src/core/user/services/user.service.ts
index c3a322c9e..8cb85e93b 100644
--- a/packages/twenty-server/src/core/user/services/user.service.ts
+++ b/packages/twenty-server/src/core/user/services/user.service.ts
@@ -49,7 +49,10 @@ export class UserService extends TypeOrmQueryService<User> {
       return;
     }
 
-    assert(workspaceMembers.length === 1, 'WorkspaceMember not found');
+    assert(
+      workspaceMembers.length === 1,
+      'WorkspaceMember not found or too many found',
+    );
 
     const userWorkspaceMember = new WorkspaceMember();
 
diff --git a/packages/twenty-server/src/database/typeorm/core/migrations/1707778127558-addUserWorkspaces.ts b/packages/twenty-server/src/database/typeorm/core/migrations/1707778127558-addUserWorkspaces.ts
new file mode 100644
index 000000000..e0e0b2013
--- /dev/null
+++ b/packages/twenty-server/src/database/typeorm/core/migrations/1707778127558-addUserWorkspaces.ts
@@ -0,0 +1,24 @@
+import { MigrationInterface, QueryRunner } from 'typeorm';
+
+export class AddUserWorkspaces1707778127558 implements MigrationInterface {
+  name = 'AddUserWorkspaces1707778127558';
+
+  public async up(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.query(
+      `CREATE TABLE "core"."userWorkspace" (
+                "id" uuid PRIMARY KEY DEFAULT uuid_generate_v4(), 
+                "userId" uuid NOT NULL REFERENCES core.user(id), 
+                "workspaceId" uuid NOT NULL REFERENCES core.workspace(id),
+                "createdAt" TIMESTAMP NOT NULL DEFAULT now(),
+                "updatedAt" TIMESTAMP NOT NULL DEFAULT now(),
+                "deletedAt" TIMESTAMP
+            )`,
+    );
+
+    await queryRunner.query(
+      `ALTER TABLE "core"."user" DROP CONSTRAINT "FK_2ec910029395fa7655621c88908"`,
+    );
+  }
+
+  public async down(): Promise<void> {}
+}