diff --git a/src/validator/constraints/comparison/unique.test.ts b/src/validator/constraints/comparison/unique.test.ts
new file mode 100644
index 0000000..48bd30e
--- /dev/null
+++ b/src/validator/constraints/comparison/unique.test.ts
@@ -0,0 +1,311 @@
+import { ConstraintContext } from '@/validator/constraint-validator';
+import { describe, expect, test } from 'vitest';
+import { unique, UniqueOptions } from './unique';
+
+describe('unique', () => {
+  describe('non-array values', () => {
+    test('validation passes when the value is undefined', () => {
+      const value = undefined;
+      const context: ConstraintContext = createContext('tags', value, { message: 'Tags must be unique' });
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(0);
+    });
+
+    test('validation fails when the value is null', () => {
+      const value = null;
+      const context: ConstraintContext = createContext('tags', value, {});
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(1);
+      expect(violations[0]).toEqual({
+        path: 'tags',
+        constraint: 'unique',
+        message: 'This value must be a list.',
+        value,
+      });
+    });
+
+    test('validation fails when the value is not an array', () => {
+      const value = 'admin';
+      const context: ConstraintContext = createContext('tags', value, {});
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(1);
+      expect(violations[0]).toEqual({
+        path: 'tags',
+        constraint: 'unique',
+        message: 'This value must be a list.',
+        value,
+      });
+    });
+  });
+
+  describe('arrays of scalars', () => {
+    test('validation passes when array elements are unique', () => {
+      const value = ['7', 7, true, null, undefined];
+      const context: ConstraintContext = createContext('tags', value, {});
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(0);
+    });
+
+    test('validation passes when the array contains a null value', () => {
+      const value = [null];
+      const context: ConstraintContext = createContext('tags', value, {});
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(0);
+    });
+
+    test('validation passes when the array contains an undefined value', () => {
+      const value = [undefined];
+      const context: ConstraintContext = createContext('tags', value, {});
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(0);
+    });
+
+    test('validation fails when an array contains duplicate null values', () => {
+      const value = [null, null];
+      const context: ConstraintContext = createContext('tags', value, {});
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(1);
+      expect(violations[0]).toEqual({
+        path: 'tags',
+        constraint: 'unique',
+        message: 'This value must contain only unique items.',
+        value,
+      });
+    });
+
+    test('validation fails when an array contains duplicate undefined values', () => {
+      const value = [undefined, undefined];
+      const context: ConstraintContext = createContext('tags', value, {});
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(1);
+      expect(violations[0]).toEqual({
+        path: 'tags',
+        constraint: 'unique',
+        message: 'This value must contain only unique items.',
+        value,
+      });
+    });
+
+    test('validation fails when an array contains duplicate elements', () => {
+      const value = ['admin', 'editor', 'admin'];
+      const context: ConstraintContext = createContext('tags', value, {});
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(1);
+      expect(violations[0]).toEqual({
+        path: 'tags',
+        constraint: 'unique',
+        message: 'This value must contain only unique items.',
+        value,
+      });
+    });
+  });
+
+  describe('arrays of arrays', () => {
+    test('validation passes when nested arrays have different values', () => {
+      const value = [['admin'], ['editor']];
+      const context: ConstraintContext = createContext('tags', value, {});
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(0);
+    });
+
+    test('validation fails when nested arrays have the same values', () => {
+      const value = [['admin'], ['admin']];
+      const context: ConstraintContext = createContext('tags', value, {});
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(1);
+      expect(violations[0]).toEqual({
+        path: 'tags',
+        constraint: 'unique',
+        message: 'This value must contain only unique items.',
+        value,
+      });
+    });
+  });
+
+  describe('arrays of objects', () => {
+    test('validation passes when objects have different values', () => {
+      const value = [{ id: 1 }, { id: 2 }];
+      const context: ConstraintContext = createContext('tags', value, {});
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(0);
+    });
+
+    test('validation fails when objects have the same values', () => {
+      const value = [{ id: 1 }, { id: 1 }];
+      const context: ConstraintContext = createContext('tags', value, {});
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(1);
+      expect(violations[0]).toEqual({
+        path: 'tags',
+        constraint: 'unique',
+        message: 'This value must contain only unique items.',
+        value,
+      });
+    });
+
+    test('validation passes when the configured field combinations are unique', () => {
+      const value = [
+        { latitude: 10, longitude: 20, label: 'first', name: 'first-location' },
+        { latitude: 10, longitude: 30, label: 'first', name: 'last-location' },
+      ];
+      const context: ConstraintContext = createContext('coordinates', value, {
+        fields: ['latitude', 'longitude', 'label'],
+      });
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(0);
+    });
+
+    test('validation fails when the configured field combinations contain duplicates', () => {
+      const value = [
+        { latitude: 10, longitude: 20, label: 'first', name: 'first-location' },
+        { latitude: 10, longitude: 20, label: 'first', name: 'last-location' },
+      ];
+      const context: ConstraintContext = createContext('coordinates', value, {
+        fields: ['latitude', 'longitude', 'label'],
+      });
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(1);
+      expect(violations[0]).toEqual({
+        path: 'coordinates',
+        constraint: 'unique',
+        message: 'This value must contain only unique items.',
+        value,
+      });
+    });
+
+    test('validation fails when fields are configured and an element is not an object', () => {
+      const value = [{ id: 1 }, 'admin'];
+      const context: ConstraintContext = createContext('tags', value, {
+        fields: ['id'],
+      });
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(1);
+      expect(violations[0]).toEqual({
+        path: 'tags',
+        constraint: 'unique',
+        message: 'This value must be a list of objects.',
+        value,
+      });
+    });
+  });
+
+  describe('options', () => {
+    test('validation uses a custom message when it fails', () => {
+      const value = ['admin', 'admin'];
+      const context: ConstraintContext = createContext('tags', value, { message: 'Tags must be unique' });
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(1);
+      expect(violations[0]).toEqual({
+        path: 'tags',
+        constraint: 'unique',
+        message: 'Tags must be unique',
+        value,
+      });
+    });
+
+    test('validation normalizes each array element before checking uniqueness', () => {
+      const value = ['    admin ', 'admin'];
+      const context: ConstraintContext = createContext('tags', value, {
+        normalizer: (element: unknown) => (typeof element === 'string' ? element.trim() : element),
+      });
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(1);
+      expect(violations[0]).toEqual({
+        path: 'tags',
+        constraint: 'unique',
+        message: 'This value must contain only unique items.',
+        value,
+      });
+    });
+
+    test('validation normalizes each object before checking configured field combinations', () => {
+      const value = [
+        { latitude: 10, longitude: 20, label: '     first', name: 'first-location' },
+        { latitude: 10, longitude: 20, label: 'first', name: 'last-location' },
+      ];
+      const context: ConstraintContext = createContext('coordinates', value, {
+        fields: ['latitude', 'longitude', 'label'],
+        normalizer: (element: unknown) =>
+          typeof element === 'object' && element !== null && 'label' in element
+            ? { ...element, label: String(element.label).trim() }
+            : element,
+      });
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(1);
+      expect(violations[0]).toEqual({
+        path: 'coordinates',
+        constraint: 'unique',
+        message: 'This value must contain only unique items.',
+        value,
+      });
+    });
+
+    test('validation fails when fields are configured and normalization returns a non-object element', () => {
+      const value = [{ id: 1 }, { id: 2 }];
+      const context: ConstraintContext = createContext('tags', value, {
+        fields: ['id'],
+        normalizer: (element: unknown) =>
+          typeof element === 'object' && element !== null && 'id' in element && element.id === 2 ? 'admin' : element,
+      });
+
+      const violations = unique(value, context);
+
+      expect(violations).toHaveLength(1);
+      expect(violations[0]).toEqual({
+        path: 'tags',
+        constraint: 'unique',
+        message: 'This value must be a list of objects.',
+        value,
+      });
+    });
+  });
+
+  function createContext(path: string, value: unknown, options: UniqueOptions): ConstraintContext<UniqueOptions> {
+    return {
+      path,
+      root: { [path]: value },
+      value,
+      constraint: 'unique',
+      options,
+      runNestedRules: () => [],
+    };
+  }
+});
diff --git a/src/validator/constraints/comparison/unique.ts b/src/validator/constraints/comparison/unique.ts
new file mode 100644
index 0000000..25693cc
--- /dev/null
+++ b/src/validator/constraints/comparison/unique.ts
@@ -0,0 +1,60 @@
+import { ConstraintOptions } from '@/validator/constraint';
+import { ConstraintContext } from '@/validator/constraint-validator';
+import { Violation } from '@/validator/violation';
+import { isDeepStrictEqual } from 'node:util';
+
+const DEFAULT_MESSAGE = 'This value must contain only unique items.';
+const NOT_ARRAY_MESSAGE = 'This value must be a list.';
+const FIELDS_REQUIRE_OBJECTS_MESSAGE = 'This value must be a list of objects.';
+
+export type UniqueOptions = ConstraintOptions<{
+  message?: string;
+  normalizer?: (value: unknown) => unknown;
+  fields?: string[];
+}>;
+
+const createViolation = (value: unknown, context: ConstraintContext, message: string): Violation => ({
+  path: context.path,
+  constraint: context.constraint,
+  message,
+  value,
+});
+
+const pickFields = (value: Record<string, unknown>, fields: string[]): Record<string, unknown> =>
+  Object.fromEntries(fields.map(field => [field, value[field]]));
+
+const normalizeElements = (value: unknown[], normalizer?: (value: unknown) => unknown): unknown[] =>
+  normalizer ? value.map(element => normalizer(element)) : value;
+
+const hasConfiguredFields = (fields?: string[]): fields is string[] => fields !== undefined && fields.length > 0;
+
+const isRecord = (value: unknown): value is Record<string, unknown> =>
+  typeof value === 'object' && value !== null && !Array.isArray(value);
+
+const containsOnlyRecords = (values: unknown[]): values is Record<string, unknown>[] => values.every(isRecord);
+
+const prepareComparableElements = (value: unknown[], fields?: string[]): unknown[] =>
+  hasConfiguredFields(fields) ? value.map(element => pickFields(element as Record<string, unknown>, fields)) : value;
+
+const hasOnlyUniqueValues = (values: unknown[]): boolean =>
+  values.every((value, index) =>
+    values.every((candidate, candidateIndex) => candidateIndex <= index || !isDeepStrictEqual(value, candidate)),
+  );
+
+export function unique(value: unknown, context: ConstraintContext<UniqueOptions>): Violation[] {
+  if (value === undefined) return [];
+
+  if (!Array.isArray(value)) return [createViolation(value, context, context.options.message ?? NOT_ARRAY_MESSAGE)];
+
+  const normalizedElements = normalizeElements(value, context.options.normalizer);
+
+  if (hasConfiguredFields(context.options.fields) && !containsOnlyRecords(normalizedElements)) {
+    return [createViolation(value, context, context.options.message ?? FIELDS_REQUIRE_OBJECTS_MESSAGE)];
+  }
+
+  const comparableElements = prepareComparableElements(normalizedElements, context.options.fields);
+
+  if (hasOnlyUniqueValues(comparableElements)) return [];
+
+  return [createViolation(value, context, context.options.message ?? DEFAULT_MESSAGE)];
+}
diff --git a/src/validator/constraints/index.ts b/src/validator/constraints/index.ts
index 75a267c..5aea751 100644
--- a/src/validator/constraints/index.ts
+++ b/src/validator/constraints/index.ts
@@ -1,13 +1,17 @@
 import { notBlank } from '@/validator/constraints/basic/not-blank';
+import { type } from '@/validator/constraints/basic/type';
+import { unique } from '@/validator/constraints/comparison/unique';
 import { email } from '@/validator/constraints/string/email';
 import { slug } from '@/validator/constraints/string/slug';
-import { type } from '@/validator/constraints/basic/type';
 
 export const builtInConstraints = {
   // Basic
   notBlank,
   type,
 
+  // Comparison
+  unique,
+
   // String
   email,
   slug,
@@ -17,4 +21,5 @@ export * from './string/email';
 export * from './string/slug';
 export * from './basic/not-blank';
 export * from './basic/type';
+export { unique, type UniqueOptions } from './comparison/unique';
 export * from './other/compound';