diff --git a/apps/web/src/locales/en/messages.json b/apps/web/src/locales/en/messages.json
index d6a871895f4..8325d905e18 100644
--- a/apps/web/src/locales/en/messages.json
+++ b/apps/web/src/locales/en/messages.json
@@ -5568,6 +5568,9 @@
   "domainVerified": {
     "message": "Domain verified"
   },
+  "duplicateDomainError": {
+    "message": "You can't claim the same domain twice."
+  },
   "domainNotVerified": {
     "message": "$DOMAIN$ not verified. Check your DNS record.",
     "placeholders": {
@@ -5577,5 +5580,4 @@
       }
     }
   }
-
 }
diff --git a/bitwarden_license/bit-web/src/app/organizations/manage/domain-verification/domain-add-edit-dialog/domain-add-edit-dialog.component.ts b/bitwarden_license/bit-web/src/app/organizations/manage/domain-verification/domain-add-edit-dialog/domain-add-edit-dialog.component.ts
index bce006ae006..4fcc521ee64 100644
--- a/bitwarden_license/bit-web/src/app/organizations/manage/domain-verification/domain-add-edit-dialog/domain-add-edit-dialog.component.ts
+++ b/bitwarden_license/bit-web/src/app/organizations/manage/domain-verification/domain-add-edit-dialog/domain-add-edit-dialog.component.ts
@@ -11,6 +11,7 @@ import { Utils } from "@bitwarden/common/misc/utils";
 import { OrganizationDomainRequest } from "@bitwarden/common/services/organization-domain/requests/organization-domain.request";
 
 import { domainNameValidator } from "./domain-name.validator";
+import { uniqueInArrayValidator } from "./unique-in-array.validator";
 export interface DomainAddEditDialogData {
   organizationId: string;
   orgDomain: OrganizationDomainResponse;
@@ -26,11 +27,17 @@ export class DomainAddEditDialogComponent implements OnInit {
   disablePadding = false;
 
   // TODO: should invalidDomainNameMessage have something like: "'https://', 'http://', or 'www.' domain prefixes not allowed."
-  // TODO: write separate uniqueIn validator w/ translated msg: "You can’t claim the same domain twice."
   domainForm: FormGroup = this.formBuilder.group({
     domainName: [
       "",
-      [Validators.required, domainNameValidator(this.i18nService.t("invalidDomainNameMessage"))],
+      [
+        Validators.required,
+        domainNameValidator(this.i18nService.t("invalidDomainNameMessage")),
+        uniqueInArrayValidator(
+          this.data.existingDomainNames,
+          this.i18nService.t("duplicateDomainError")
+        ),
+      ],
     ],
     txt: [{ value: null, disabled: true }],
   });
diff --git a/bitwarden_license/bit-web/src/app/organizations/manage/domain-verification/domain-add-edit-dialog/unique-in-array.validator.ts b/bitwarden_license/bit-web/src/app/organizations/manage/domain-verification/domain-add-edit-dialog/unique-in-array.validator.ts
new file mode 100644
index 00000000000..4659a265959
--- /dev/null
+++ b/bitwarden_license/bit-web/src/app/organizations/manage/domain-verification/domain-add-edit-dialog/unique-in-array.validator.ts
@@ -0,0 +1,23 @@
+import { AbstractControl, ValidationErrors, ValidatorFn } from "@angular/forms";
+export function uniqueInArrayValidator(values: Array<string>, errorMessage: string): ValidatorFn {
+  return (control: AbstractControl): ValidationErrors | null => {
+    const value = control.value;
+
+    if (!value) {
+      return null;
+    }
+
+    const lowerTrimmedValue = value.toLowerCase().trim();
+
+    // check if the entered value is unique
+    if (values.some((val) => val.toLowerCase().trim() === lowerTrimmedValue)) {
+      return {
+        nonUniqueValue: {
+          message: errorMessage,
+        },
+      };
+    }
+
+    return null;
+  };
+}
diff --git a/bitwarden_license/bit-web/src/app/organizations/manage/domain-verification/domain-verification.component.ts b/bitwarden_license/bit-web/src/app/organizations/manage/domain-verification/domain-verification.component.ts
index 607da81becc..e8b9b4012cd 100644
--- a/bitwarden_license/bit-web/src/app/organizations/manage/domain-verification/domain-verification.component.ts
+++ b/bitwarden_license/bit-web/src/app/organizations/manage/domain-verification/domain-verification.component.ts
@@ -1,6 +1,6 @@
 import { Component, OnDestroy, OnInit } from "@angular/core";
 import { ActivatedRoute, Params } from "@angular/router";
-import { concatMap, Observable, Subject, takeUntil } from "rxjs";
+import { concatMap, Observable, Subject, take, takeUntil } from "rxjs";
 
 import { ApiService } from "@bitwarden/common/abstractions/api.service";
 import { I18nService } from "@bitwarden/common/abstractions/i18n.service";
@@ -68,7 +68,7 @@ export class DomainVerificationComponent implements OnInit, OnDestroy {
     const domainAddEditDialogData: DomainAddEditDialogData = {
       organizationId: this.organizationId,
       orgDomain: null,
-      existingDomainNames: [],
+      existingDomainNames: this.getExistingDomainNames(),
     };
 
     this.dialogService.open(DomainAddEditDialogComponent, {
@@ -80,7 +80,7 @@ export class DomainVerificationComponent implements OnInit, OnDestroy {
     const domainAddEditDialogData: DomainAddEditDialogData = {
       organizationId: this.organizationId,
       orgDomain: orgDomain,
-      existingDomainNames: [],
+      existingDomainNames: this.getExistingDomainNames(),
     };
 
     this.dialogService.open(DomainAddEditDialogComponent, {
@@ -88,6 +88,15 @@ export class DomainVerificationComponent implements OnInit, OnDestroy {
     });
   }
 
+  private getExistingDomainNames(): Array<string> {
+    let existingDomainNames: string[];
+    // eslint-disable-next-line rxjs-angular/prefer-takeuntil
+    this.orgDomains$.pipe(take(1)).subscribe((orgDomains: Array<OrganizationDomainResponse>) => {
+      existingDomainNames = orgDomains.map((o) => o.domainName);
+    });
+    return existingDomainNames;
+  }
+
   ngOnDestroy(): void {
     this.componentDestroyed$.next();
     this.componentDestroyed$.complete();