[1] Born in Carmarthen, Williams attended Coleg Sir Gar,[2] and is a fluent Welsh speaker.

After impressive performances off the bench against England at Twickenham and the Millennium Stadium, Williams was chosen as one of four centres in the final 30 man squad for the 2011 Rugby World Cup in New Zealand.

Williams replaced the injured Jamie Roberts at half-time at Twickenham on 25 February 2012 in Wales' third Six Nations victory against England.

He scored a solo try from the half-way line, having ripped the ball from England forward Courtney Lawes.

[16] In 2021, Williams was briefly recalled to the Welsh squad, after Willis Halaholo tested positive for coronavirus.