On 17 January 2023 he was appointed as an Assistant Coach of the Welsh rugby union team.

With the regionalisation of Welsh rugby in 2003, Swansea combined with Neath to form the Ospreys, where over a 10-year period Thomas won four league titles and an Anglo-Welsh Cup.

On 28 May 2013, Thomas joined English team Worcester Warriors from the 2013–14 season.

Thomas was part of two Six Nations Grand Slams, in 2005, and in 2008 where he started every game.

Thomas joined Bristol Rugby ahead of the 2016/17 campaign as Defence and Forwards Coach.