diff --git a/src/backend/core/migrations/0006_merge_duplicate_users.py b/src/backend/core/migrations/0006_merge_duplicate_users.py
new file mode 100644
index 00000000..fd1217a3
--- /dev/null
+++ b/src/backend/core/migrations/0006_merge_duplicate_users.py
@@ -0,0 +1,89 @@
+
+from django.db import migrations
+from django.db.models import Count
+from core.models import RoleChoices
+
+def merge_duplicate_user_accounts(apps, schema_editor):
+    """Merge user accounts that share the same email address.
+
+    Historical Context:
+    Previously, ProConnect authentication could return users with the same email
+    but different sub, leading to duplicate user accounts. While the application
+    now prevents this scenario, this migration is needed to clean up existing
+    duplicate accounts to ensure users can continue to connect without being blocked
+    by unique email constraints.
+
+    Performance of this migration is poor, this implementation prioritizes readability
+    and maintainability. Consider refactoring this code to avoid individual db queries
+    on each iteration.
+    """
+
+    User = apps.get_model('core', 'User')
+    ResourceAccess = apps.get_model('core', 'ResourceAccess')
+
+    emails_with_duplicates = (
+        User.objects.values('email')
+        .annotate(count=Count('id'))
+        .filter(count__gt=1)
+        .values_list('email', flat=True)
+    )
+
+    for email in emails_with_duplicates:
+        # Keep the oldest user
+        primary_user = User.objects.filter(email=email).order_by('created_at').first()
+        duplicate_user_accounts = User.objects.filter(email=email).exclude(id=primary_user.id)
+
+        # Get IDs of duplicate accounts to be merged
+        duplicate_account_ids = list(duplicate_user_accounts.values_list('id', flat=True))
+        resource_accesses_to_transfer = ResourceAccess.objects.filter(user_id__in=duplicate_account_ids)
+
+        # Transfer resource access permissions to primary user
+        # This process handles role hierarchy where:
+        # OWNER > ADMIN > MEMBER
+        for resource_access in resource_accesses_to_transfer:
+
+            # Determine if primary user already has access to this resource
+            existing_primary_access = ResourceAccess.objects.filter(
+                user_id=primary_user.id,
+                resource_id=resource_access.resource.id
+            ).first()
+
+            if existing_primary_access:
+                # Skip if primary user is already OWNER as it's the highest privilege level
+                # No need to modify or downgrade owner access
+                if existing_primary_access.role == RoleChoices.OWNER:
+                    continue
+
+                # Skip if primary user already has the exact same role
+                # No need to update when roles match
+                elif existing_primary_access.role == resource_access.role:
+                    continue
+
+                # Skip if new role is MEMBER since user already has base access
+                # All existing access includes at least MEMBER privileges
+                elif resource_access.role == RoleChoices.MEMBER:
+                    continue
+
+                # Update the role only if it represents a higher privilege level
+                # Preserves existing access record while updating the role
+                existing_primary_access.role = resource_access.role
+                existing_primary_access.save()
+            else:
+                # Transfer access to primary user
+                resource_access.user_id = primary_user.id
+                resource_access.save()
+
+        # Delete duplicate accounts - CASCADE will automatically remove any untransferred
+        # ResourceAccess records and other related data for these users
+        duplicate_user_accounts.delete()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0005_recording_recordingaccess_and_more'),
+    ]
+
+    operations = [
+        migrations.RunPython(merge_duplicate_user_accounts, reverse_code=migrations.RunPython.noop),
+    ]