Williams started his career as a scrum half at Amman United, later moving to Neath and to the wing. He currently plays regional rugby with the Ospreys.

Williams was also one of the stars of the 2005 RBS 6 Nations campaign and toured New Zealand with the Lions in 2005.

Shane Williams became Wales’ all-time leading try scorer in the Grand Slam winning 2008 RBS 6 Nations campaign, after breaking Gareth Thomas's record with his 41st Test score in just 56 appearances. The outstanding performer in the 2008 championship, the wing wizard gained the RBS 6 Nations Player of the Tournament accolade to cap his superb performances.

Williams was included in the starting line-up for all of Wales’ at the 2007 Rugby World Cup, and enjoyed a successful personal tournament scoring six tries in total, making him the joint third highest try scorer of the entire tournament (on a par with Doug Howlett, behind Bryan Habana and Drew Mitchell).

In January 2008 Williams was included RBS 6 Nations squad, and the winger proved a revelation in the championship. Williams amassed an impressive six tries, equalling Will Greenwood's Six Nations try-scoring record (in the Lloyds TSB Six Nations, 2001), playing in all five matches of the Grand Slam campaign and gaining braces against Scotland and Italy, and single efforts against Ireland and France. He was voted the player of the tournament and in the process he also managed to surpass Gareth Thomas’s Wales try-scoring record.

He was voted the IRB Player of the Year in November 2008.