After seven years with Scarlets, Williams also had spells with the likes of Saracens and Cardiff before joining Newcastle Red Bull last year.
Williams will continue to play for Newcastle but, confirming his international retirement with a post on Instagram, he said: “I have decided that the time has come to say goodbye.
“From working as a scaffolder in Port Talbot steelworks, to pulling on that famous red jersey.
“It’s been a journey built on hard work, sacrifice and the support of so many people along the way.
“The dedicated and loyal Welsh fans. Amazing team-mates, great coaches, the backroom staff and friends.
“To also represent the British and Irish Lions on two tours, and earn five caps, is an experience I’ll always be grateful for.
“I step away from international rugby with no regrets, only pride and gratitude for the opportunity given to me. Diolch.”
