diff --git a/src/Symfony/Component/Validator/CHANGELOG.md b/src/Symfony/Component/Validator/CHANGELOG.md
index 509f331767..54d6120a21 100644
--- a/src/Symfony/Component/Validator/CHANGELOG.md
+++ b/src/Symfony/Component/Validator/CHANGELOG.md
@@ -8,6 +8,7 @@ CHANGELOG
  * added UATP cards support to `CardSchemeValidator`
  * added option `allowNull` to NotBlank constraint
  * added `Json` constraint
+ * added `Unique` constraint
  
 4.2.0
 -----
diff --git a/src/Symfony/Component/Validator/Constraints/Unique.php b/src/Symfony/Component/Validator/Constraints/Unique.php
new file mode 100644
index 0000000000..391c4eaa13
--- /dev/null
+++ b/src/Symfony/Component/Validator/Constraints/Unique.php
@@ -0,0 +1,31 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Validator\Constraints;
+
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * @Annotation
+ * @Target({"PROPERTY", "METHOD", "ANNOTATION"})
+ *
+ * @author Yevgeniy Zholkevskiy <zhenya.zholkevskiy@gmail.com>
+ */
+class Unique extends Constraint
+{
+    public const IS_NOT_UNIQUE = '7911c98d-b845-4da0-94b7-a8dac36bc55a';
+
+    protected static $errorNames = [
+        self::IS_NOT_UNIQUE => 'IS_NOT_UNIQUE',
+    ];
+
+    public $message = 'This collection should contain only unique elements';
+}
diff --git a/src/Symfony/Component/Validator/Constraints/UniqueValidator.php b/src/Symfony/Component/Validator/Constraints/UniqueValidator.php
new file mode 100644
index 0000000000..72403b59bd
--- /dev/null
+++ b/src/Symfony/Component/Validator/Constraints/UniqueValidator.php
@@ -0,0 +1,53 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Validator\Constraints;
+
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+use Symfony\Component\Validator\Exception\UnexpectedValueException;
+
+/**
+ * @author Yevgeniy Zholkevskiy <zhenya.zholkevskiy@gmail.com>
+ */
+class UniqueValidator extends ConstraintValidator
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function validate($value, Constraint $constraint)
+    {
+        if (!$constraint instanceof Unique) {
+            throw new UnexpectedTypeException($constraint, Unique::class);
+        }
+
+        if (null === $value) {
+            return;
+        }
+
+        if (!\is_array($value) && !$value instanceof \IteratorAggregate) {
+            throw new UnexpectedValueException($value, 'array|IteratorAggregate');
+        }
+
+        $collectionElements = [];
+        foreach ($value as $element) {
+            if (\in_array($element, $collectionElements, true)) {
+                $this->context->buildViolation($constraint->message)
+                    ->setParameter('{{ value }}', $this->formatValue($value))
+                    ->setCode(Unique::IS_NOT_UNIQUE)
+                    ->addViolation();
+
+                return;
+            }
+            $collectionElements[] = $element;
+        }
+    }
+}
diff --git a/src/Symfony/Component/Validator/Tests/Constraints/UniqueValidatorTest.php b/src/Symfony/Component/Validator/Tests/Constraints/UniqueValidatorTest.php
new file mode 100644
index 0000000000..65564abf9c
--- /dev/null
+++ b/src/Symfony/Component/Validator/Tests/Constraints/UniqueValidatorTest.php
@@ -0,0 +1,89 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Validator\Tests\Constraints;
+
+use Symfony\Component\Validator\Constraints\Unique;
+use Symfony\Component\Validator\Constraints\UniqueValidator;
+use Symfony\Component\Validator\Test\ConstraintValidatorTestCase;
+
+class UniqueValidatorTest extends ConstraintValidatorTestCase
+{
+    protected function createValidator()
+    {
+        return new UniqueValidator();
+    }
+
+    /**
+     * @expectedException \Symfony\Component\Validator\Exception\UnexpectedValueException
+     */
+    public function testExpectsUniqueConstraintCompatibleType()
+    {
+        $this->validator->validate('', new Unique());
+    }
+
+    /**
+     * @dataProvider getValidValues
+     */
+    public function testValidValues($value)
+    {
+        $this->validator->validate($value, new Unique());
+
+        $this->assertNoViolation();
+    }
+
+    public function getValidValues()
+    {
+        return [
+            yield 'null' => [[null]],
+            yield 'empty array' => [[]],
+            yield 'single integer' => [[5]],
+            yield 'single string' => [['a']],
+            yield 'single object' => [[new \stdClass()]],
+            yield 'unique booleans' => [[true, false]],
+            yield 'unique integers' => [[1, 2, 3, 4, 5, 6]],
+            yield 'unique floats' => [[0.1, 0.2, 0.3]],
+            yield 'unique strings' => [['a', 'b', 'c']],
+            yield 'unique arrays' => [[[1, 2], [2, 4], [4, 6]]],
+            yield 'unique objects' => [[new \stdClass(), new \stdClass()]],
+        ];
+    }
+
+    /**
+     * @dataProvider getInvalidValues
+     */
+    public function testInvalidValues($value)
+    {
+        $constraint = new Unique([
+            'message' => 'myMessage',
+        ]);
+        $this->validator->validate($value, $constraint);
+
+        $this->buildViolation('myMessage')
+             ->setParameter('{{ value }}', 'array')
+             ->setCode(Unique::IS_NOT_UNIQUE)
+             ->assertRaised();
+    }
+
+    public function getInvalidValues()
+    {
+        $object = new \stdClass();
+
+        return [
+            yield 'not unique booleans' => [[true, true]],
+            yield 'not unique integers' => [[1, 2, 3, 3]],
+            yield 'not unique floats' => [[0.1, 0.2, 0.1]],
+            yield 'not unique string' => [['a', 'b', 'a']],
+            yield 'not unique arrays' => [[[1, 1], [2, 3], [1, 1]]],
+            yield 'not unique objects' => [[$object, $object]],
+        ];
+    }
+}