Thomas made his senior debut for Swansea on 19 September 2012, coming on as a replacement in a 14–25 home loss to Cross Keys.[3] Thomas impressed many with his performances for Swansea during the 2012–13 season and earned a call-up to the Ospreysregional team, making his professional debut on 9 November 2012 in a 33–27 win against Gloucester in the LV= Cup.[4]
On 28 January 2015, it was announced Thomas would be joining Gloucester at the start of the 2015–16 season.[5]
On 19 October 2016, it was announced that Thomas would be joining the Scarlets from Gloucester with immediate effect.[2]
On 9 March 2020, Thomas would rejoin his home region Ospreys on a two-year deal in the Pro14 from the 2020–21 season.[7] He joined Premiership Rugby side Wasps on a short-term deal in February 2021.[8]