On 30 June 2015, Mawson signed for League One club Barnsley on a three-year deal [REF].
On 30 August 2016, after just four league games experience in the Football League Championship with Barnsley, Mawson signed for Premier League side Swansea City on a four-year deal worth £5.5 million[REF], taking the number 6 shirt to replace club hero Ashley Williams.