diff --git a/apps/lfx-one/src/app/modules/project/settings/components/user-form/user-form.component.html b/apps/lfx-one/src/app/modules/project/settings/components/user-form/user-form.component.html
index 537b3860..00327859 100644
--- a/apps/lfx-one/src/app/modules/project/settings/components/user-form/user-form.component.html
+++ b/apps/lfx-one/src/app/modules/project/settings/components/user-form/user-form.component.html
@@ -4,19 +4,19 @@
 <form [formGroup]="form()" (ngSubmit)="onSubmit()" class="space-y-6">
   <!-- User Information Section -->
   <div class="flex flex-col gap-3">
-    <!-- Username -->
+    <!-- Username or Email -->
     <div>
-      <label for="username" class="block text-sm font-medium text-gray-700 mb-1"> Username <span class="text-red-500">*</span> </label>
+      <label for="username" class="block text-sm font-medium text-gray-700 mb-1"> Username or Email <span class="text-red-500">*</span> </label>
       <lfx-input-text
         size="small"
         [form]="form()"
         control="username"
         id="username"
-        placeholder="Enter username"
+        placeholder="Enter username or email address"
         styleClass="w-full"
         data-testid="settings-user-form-username"></lfx-input-text>
       @if (form().get('username')?.errors?.['required'] && form().get('username')?.touched) {
-        <p class="mt-1 text-xs text-red-600">Username is required</p>
+        <p class="mt-1 text-xs text-red-600">Username or email is required</p>
       }
     </div>
   </div>
diff --git a/apps/lfx-one/src/app/modules/project/settings/components/user-form/user-form.component.ts b/apps/lfx-one/src/app/modules/project/settings/components/user-form/user-form.component.ts
index daac58e4..bd4468f8 100644
--- a/apps/lfx-one/src/app/modules/project/settings/components/user-form/user-form.component.ts
+++ b/apps/lfx-one/src/app/modules/project/settings/components/user-form/user-form.component.ts
@@ -1,6 +1,7 @@
 // Copyright The Linux Foundation and each contributor to LFX.
 // SPDX-License-Identifier: MIT
 
+import { HttpErrorResponse } from '@angular/common/http';
 import { Component, computed, inject, signal } from '@angular/core';
 import { FormControl, FormGroup, ReactiveFormsModule, Validators } from '@angular/forms';
 import { ButtonComponent } from '@components/button/button.component';
@@ -92,13 +93,29 @@ export class UserFormComponent {
         });
         this.dialogRef.close(true);
       },
-      error: (error: any) => {
+      error: (error: HttpErrorResponse) => {
         console.error('Error saving user:', error);
-        this.messageService.add({
-          severity: 'error',
-          summary: 'Error',
-          detail: `Failed to ${this.isEditing() ? 'update' : 'add'} user. Please try again.`,
-        });
+
+        // Check if it's a 404 error for email not found
+        if (error.status === 404 && error.error?.code === 'NOT_FOUND') {
+          const usernameValue = formValue.username;
+          const isEmail = usernameValue.includes('@');
+
+          this.messageService.add({
+            severity: 'error',
+            summary: 'User Not Found',
+            detail: isEmail
+              ? `No user found with email address "${usernameValue}". Please verify the email address and try again.`
+              : error.error?.message || 'User not found',
+          });
+        } else {
+          this.messageService.add({
+            severity: 'error',
+            summary: 'Error',
+            detail: error.error?.message || `Failed to ${this.isEditing() ? 'update' : 'add'} user. Please try again.`,
+          });
+        }
+
         this.submitting.set(false);
       },
     });
diff --git a/apps/lfx-one/src/server/controllers/project.controller.ts b/apps/lfx-one/src/server/controllers/project.controller.ts
index 19aaba02..a05b7346 100644
--- a/apps/lfx-one/src/server/controllers/project.controller.ts
+++ b/apps/lfx-one/src/server/controllers/project.controller.ts
@@ -259,12 +259,39 @@ export class ProjectController {
         return;
       }
 
-      const result = await this.projectService.updateProjectPermissions(req, uid, 'add', userData.username, userData.role);
+      // Detect if input is email or username
+      const isEmail = userData.username.includes('@');
+      let username = userData.username;
+
+      if (isEmail) {
+        req.log.info(
+          {
+            email: userData.username,
+            operation: 'add_user_project_permissions',
+          },
+          'Email detected, resolving to username via NATS'
+        );
+
+        // Resolve email to username via NATS
+        username = await this.projectService.resolveEmailToUsername(req, userData.username);
+
+        req.log.info(
+          {
+            email: userData.username,
+            username,
+            operation: 'add_user_project_permissions',
+          },
+          'Successfully resolved email to username'
+        );
+      }
+
+      const result = await this.projectService.updateProjectPermissions(req, uid, 'add', username, userData.role);
 
       Logger.success(req, 'add_user_project_permissions', startTime, {
         uid,
-        username: userData.username,
+        username,
         role: userData.role,
+        resolved_from_email: isEmail,
       });
 
       res.status(201).json(result);
diff --git a/apps/lfx-one/src/server/services/project.service.ts b/apps/lfx-one/src/server/services/project.service.ts
index 7ee3e5df..7df4153c 100644
--- a/apps/lfx-one/src/server/services/project.service.ts
+++ b/apps/lfx-one/src/server/services/project.service.ts
@@ -207,6 +207,91 @@ export class ProjectService {
     return result;
   }
 
+  /**
+   * Resolve email address to username using NATS request-reply pattern
+   * @param req - Express request object for logging
+   * @param email - Email address to lookup
+   * @returns Username associated with the email
+   * @throws ResourceNotFoundError if user not found
+   */
+  public async resolveEmailToUsername(req: Request, email: string): Promise<string> {
+    const codec = this.natsService.getCodec();
+
+    // Normalize email input
+    const normalizedEmail = email.trim().toLowerCase();
+
+    try {
+      req.log.info({ email: normalizedEmail }, 'Resolving email to username via NATS');
+
+      const response = await this.natsService.request(NatsSubjects.EMAIL_TO_USERNAME, codec.encode(normalizedEmail), { timeout: NATS_CONFIG.REQUEST_TIMEOUT });
+
+      const responseText = codec.decode(response.data);
+
+      // Parse once and branch on the result shape
+      let username: string;
+      try {
+        const parsed = JSON.parse(responseText);
+
+        // Check if it's an error response
+        if (typeof parsed === 'object' && parsed !== null && parsed.success === false) {
+          req.log.info({ email: normalizedEmail, error: parsed.error }, 'User email not found via NATS');
+
+          throw new ResourceNotFoundError('User', normalizedEmail, {
+            operation: 'resolve_email_to_username',
+            service: 'project_service',
+            path: '/nats/email-to-username',
+          });
+        }
+
+        // Extract username from JSON success response or JSON string
+        username = typeof parsed === 'string' ? parsed : parsed.username;
+      } catch (parseError) {
+        // Re-throw ResourceNotFoundError as-is
+        if (parseError instanceof ResourceNotFoundError) {
+          throw parseError;
+        }
+
+        // JSON parsing failed - use raw text as username
+        username = responseText;
+      }
+
+      // Trim and validate username
+      username = username.trim();
+
+      if (!username || username === '') {
+        req.log.info({ email: normalizedEmail }, 'Empty username returned from NATS');
+
+        throw new ResourceNotFoundError('User', normalizedEmail, {
+          operation: 'resolve_email_to_username',
+          service: 'project_service',
+          path: '/nats/email-to-username',
+        });
+      }
+
+      req.log.info({ email: normalizedEmail, username }, 'Successfully resolved email to username');
+
+      return username;
+    } catch (error) {
+      // Re-throw ResourceNotFoundError as-is
+      if (error instanceof ResourceNotFoundError) {
+        throw error;
+      }
+
+      req.log.error({ error: error instanceof Error ? error.message : error, email: normalizedEmail }, 'Failed to resolve email to username via NATS');
+
+      // If it's a timeout or no responder error, treat as not found
+      if (error instanceof Error && (error.message.includes('timeout') || error.message.includes('503'))) {
+        throw new ResourceNotFoundError('User', normalizedEmail, {
+          operation: 'resolve_email_to_username',
+          service: 'project_service',
+          path: '/nats/email-to-username',
+        });
+      }
+
+      throw error;
+    }
+  }
+
   /**
    * Get project ID by slug using NATS request-reply pattern
    * @private
diff --git a/packages/shared/src/enums/nats.enum.ts b/packages/shared/src/enums/nats.enum.ts
index 5cd1f2d4..e4435e67 100644
--- a/packages/shared/src/enums/nats.enum.ts
+++ b/packages/shared/src/enums/nats.enum.ts
@@ -7,4 +7,5 @@
 export enum NatsSubjects {
   PROJECT_SLUG_TO_UID = 'lfx.projects-api.slug_to_uid',
   USER_METADATA_UPDATE = 'lfx.auth-service.user_metadata.update',
+  EMAIL_TO_USERNAME = 'lfx.auth-service.email_to_username',
 }
diff --git a/packages/shared/src/interfaces/auth.interface.ts b/packages/shared/src/interfaces/auth.interface.ts
index c9b0ec82..efa5e823 100644
--- a/packages/shared/src/interfaces/auth.interface.ts
+++ b/packages/shared/src/interfaces/auth.interface.ts
@@ -161,3 +161,14 @@ export interface AuthConfig {
   /** Default route type for unmatched routes */
   defaultType: RouteType;
 }
+
+/**
+ * Error response from email to username NATS lookup
+ * @description Response structure when user email is not found
+ */
+export interface EmailToUsernameErrorResponse {
+  /** Success flag - always false for error responses */
+  success: false;
+  /** Error message describing the failure */
+  error: string;
+}