Mason is a former chairman of the Bolton Referees' Society and is associated with the Lancashire County Football Association. His younger brother, Andy Mason, is a former professional footballer who played for Bolton Wanderers, among others.
Mason attended the Liverpool Institute of Higher Education between 1990 and 1993, living in Newman Hall, where he gained his degree. Whilst there he played for his college football team as well as being a regular compere, hosting a variety of social events at a students' union club.
Mason took up the whistle in 1988, officiating in the Bolton Boys' Federation League. He previously worked in the car rental industry. In 1992, he was added to the North West Counties Football League assistant referees' list, and progressed to referee in that league four years later. He was included on The Football League list of assistant referees in 1998, and was added to the Premier League assistant referees' list in 2000.
In 2002, he was promoted to referee in the Football League, and his first match at that level was a Third Division match between Shrewsbury Town and Exeter City in August 2002, won 1–0 by the home side.
Also in 2002, he took charge of that year's FA County Youth Cup final between Birmingham and Durham, which Birmingham won 2–1.
Mason became a Development Group referee in 2003, and finally reached the Premier League list of Select Group Referees in 2006. His first Premier League appointment came in February 2006, when Middlesbrough lost 4–0 at home to Aston Villa.
Later in 2006, he was appointed to referee the Football League One play-off final between Barnsley and Swansea City at Cardiff's Millennium Stadium, which Barnsley won on penalties after a 2–2 draw after extra time.
In 2008, Mason was widely criticised for his decision to send off Middlesbrough's Jérémie Aliadière after an altercation between Aliadière and Liverpool's Javier Mascherano, while the latter escaped any punishment. Middlesbrough appealed the red card but Aliadière's ban was not only upheld by The FA, but increased by an extra match (to a total of four) on the grounds that their appeal had been "frivolous". Middlesbrough chairman Steve Gibson called The FA "amateurs and silly little men".
In 2009, Mason refereed the FA Youth Cup final between Arsenal and Liverpool. Later that year, he was handed a one-week demotion to the role of fourth official after his handling of a match between Fulham and Liverpool in which he sent off Liverpool players Jamie Carragher and Philipp Degen; Fulham ultimately won the fixture 3–1.
Mason and his assistants came in for criticism from Manchester United's management in December 2010 for allowing a last-minute equaliser scored by Birmingham City to stand. A Birmingham cross into United's penalty area appeared to hit Nikola Žigić's arm and Lee Bowyer slid the ball home despite appearing to be offside. Birmingham manager Alex McLeish defended the decision to allow the goal, saying that Mason would have been "harsh if he had penalized [Žigić] for deliberate handball".
Mason's decision in April 2012 to send-off Shaun Derry for a professional foul in the 14th minute of a match against Manchester United was appealed by Queens Park Rangers after reviewing video replays. The referee awarded United a penalty kick when Derry appeared to foul Ashley Young. QPR manager Mark Hughes criticised Young for going to ground "too readily" and Mason for being "very quick" in giving the penalty, despite Young being in an offside position when he received the ball. However, the Football Association upheld the red card.
He was widely praised in the press following his handling of a League Cup tie between Chelsea and Manchester United in October 2012. The two teams had met three days prior in an incident-filled Premier League fixture which United won 3–2 and Chelsea had two players sent off. After that game, Chelsea made a formal complaint to The FA against referee Mark Clattenburg about his alleged use of "inappropriate language" towards two of their players. During the League Cup match, Mason correctly awarded three penalties and was required to interpret and handle a number of other incidents. Chelsea won 5–4 after a 90th-minute penalty for the Blues, who were previously 3–2 down, forced the Cup tie into extra-time.
In March 2015, Mason caused controversy during a Football League Championship match between Cardiff City and AFC Bournemouth by disallowing a goal by Bournemouth's Callum Wilson after Cardiff's goalkeeper struck a drop-kick against his back as he stood just outside the area, with the ball looping back against the crossbar before Wilson converted it. Pundits said after the game that the goal, which would have given Bournemouth a 2–1 lead, was legitimate and should have stood, while Wilson should not have been booked. The game ended 1–1.
In 2016, in a Premier League game between Stoke City and Southampton, Mason came under criticism for showing Southampton's Sadio Mané a straight red card for a challenge on Erik Pieters in the final minutes of the match. Southampton's appeal against the decision was granted and Mané's three-match ban was repealed. He was also criticised for ignoring a penalty appeal when Southampton's Dušan Tadić was fouled by Stoke goalkeeper Jack Butland in the goal area. The following match weekend, in response to this criticism, Mason was removed from refereeing duties and instead reassigned to fourth official's work.
Statistics are for all competitions. No records are available prior to 2002-03.