 In a 14-year career Mason played for four Super League teams; the Wakefield Trinity Wildcats, St Helens, the Castleford Tigers, and the Huddersfield Giants, as well as playing in the NRL for a season with Melbourne Storm.In 2009 Mason won the 'Coaches' Player of The Year', the 'Directors' Player of The Year', and the Huddersfield Giants 'Man of Steel Award', he also appeared in a challenge cup final in the same year at the Wembley stadium against Warrington wolves a boyhood dream come true for mason, also appearing in 2 more challenge cup finals in 2004 which he won for St Helens against Wigan at the millennium stadium playing .Keith Mason won caps for Wales while at Wakefield Trinity Wildcats in 2001 against England, and while at Melbourne Storm in 2002 against New Zealand on Sunday 3 November 2002.