diff --git a/README.md b/README.md
index 2372049..312d101 100644
--- a/README.md
+++ b/README.md
@@ -254,6 +254,7 @@ No modules.
 | [aws_identitystore_group.sso_groups](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/identitystore_group) | resource |
 | [aws_identitystore_group_membership.sso_group_membership](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/identitystore_group_membership) | resource |
 | [aws_identitystore_group_membership.sso_group_membership_existing_google_sso_users](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/identitystore_group_membership) | resource |
+| [aws_identitystore_group_membership.sso_group_membership_existing_sso_users](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/identitystore_group_membership) | resource |
 | [aws_identitystore_user.sso_users](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/identitystore_user) | resource |
 | [aws_ssoadmin_account_assignment.account_assignment](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/ssoadmin_account_assignment) | resource |
 | [aws_ssoadmin_application.sso_apps](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/ssoadmin_application) | resource |
diff --git a/locals.tf b/locals.tf
index d996c3d..47f5a7d 100644
--- a/locals.tf
+++ b/locals.tf
@@ -14,6 +14,20 @@ locals {
     for s in local.flatten_user_data : format("%s_%s", s.user_name, s.group_name) => s
   }
 
+  # Create a new local variable by flattening the complex type given in the variable "existing_sso_users"
+  flatten_user_data_existing_sso_users = flatten([
+    for this_existing_user in keys(var.existing_sso_users) : [
+      for group in var.existing_sso_users[this_existing_user].group_membership : {
+        user_name  = var.existing_sso_users[this_existing_user].user_name
+        group_name = group
+      }
+    ]
+  ])
+
+  users_and_their_groups_existing_sso_users = {
+    for s in local.flatten_user_data_existing_sso_users : format("%s_%s", s.user_name, s.group_name) => s
+  }
+
   # Create a new local variable by flattening the complex type given in the variable "existing_google_sso_users"
   flatten_user_data_existing_google_sso_users = flatten([
     for this_existing_google_user in keys(var.existing_google_sso_users) : [
diff --git a/main.tf b/main.tf
index 9fa2617..120c583 100644
--- a/main.tf
+++ b/main.tf
@@ -137,7 +137,17 @@ resource "aws_identitystore_group_membership" "sso_group_membership" {
   identity_store_id = local.sso_instance_id
 
   group_id  = (contains(local.this_groups, each.value.group_name) ? aws_identitystore_group.sso_groups[each.value.group_name].group_id : data.aws_identitystore_group.existing_sso_groups[each.value.group_name].group_id)
-  member_id = (contains(local.this_users, each.value.user_name) ? aws_identitystore_user.sso_users[each.value.user_name].user_id : data.aws_identitystore_user.existing_sso_users[each.value.user_name].user_id)
+  member_id = aws_identitystore_user.sso_users[each.value.user_name].user_id
+
+}
+
+# Existing Users with New Groups
+resource "aws_identitystore_group_membership" "sso_group_membership_existing_sso_users" {
+  for_each          = local.users_and_their_groups_existing_sso_users
+  identity_store_id = local.sso_instance_id
+
+  group_id  = (contains(local.this_groups, each.value.group_name) ? aws_identitystore_group.sso_groups[each.value.group_name].group_id : data.aws_identitystore_group.existing_sso_groups[each.value.group_name].group_id)
+  member_id = data.aws_identitystore_user.existing_sso_users[each.value.user_name].user_id
 
 }