Williams was born in Brighton and attended Windlesham House School.[2][3] He represented Wales at U16 and U19 levels, then switched to England for the 2002 IRB U19 World Cup.[4]
Williams started and scored a try for Harlequins in their 2011–12 Premiership final victory over Leicester Tigers.[8] He is a member of the “200 Club” having represented Harlequins for over 200 games.
He retired in 2015[2] moving into a coaching and mentoring role at Harlequins for four years before leaving professional rugby in 2019 to pursue a career in consultancy.
During the 2008–09 Heineken Cup quarter final against Leinster, Williams was told to fake a blood injury by Dean Richards to allow a tactical substitution to reintroduce Nick Evans leading to the bloodgate scandal. This resulted in a 12-month ban for Williams, (reduced to four months on appeal), a three-year ban for former rugby director Dean Richards as well as a two-year ban for physiotherapist Steph Brennan from the ERC with a £260,000 fine for the club.[9]