Early career A
centre back, Mawson joined the
Reading academy at the age of nine. He remained with the club until his release at age 15 and subsequently had unsuccessful trials with
AFC Bournemouth and
Millwall. He played for the
youth team during the
2010–11 season and progressed into the
Development Squad during the
2011–12 season, He also took over the youth team
captaincy during the latter part of the season. In April 2012, Mawson signed a two-year professional contract at Brentford. Mawson suffered an injury-hit
2012–13 season and managed only 12 Development Squad appearances. Mawson made his professional debut in a 5–0
League Cup second round defeat at
Derby County in August 2013, replacing
Sam Saunders after 73 minutes. He scored his first goal of the
2013–14 season with the opener in a 1–1
Professional Development League 2 South draw with
Brighton & Hove Albion on 16 September 2013. He scored his second goal in a 4–1 defeat to
Ipswich Town on 26 November and his third in the return fixture against Brighton & Hove Albion on 27 January 2014. Mawson made 12 appearances and scored three goals for the Development Squad during the 2013–14 season, in addition to making one first-team appearance. before signing a new one-year deal on 5 June 2014. Mawson spent the entire
2014–15 season away on loan and after excelling, he was offered a new two-year contract in April 2015. He turned the deal down and departed
Griffin Park when his contract expired on 30 June. An undisclosed compensation fee was agreed in February 2016.
Maidenhead United (loans) Mawson signed for
Conference South club
Maidenhead United on 13 December 2012 on a one-month loan, earning praise from manager
Johnson Hippolyte for his performance on his debut in a 1–0 win against
Truro City. Mawson returned to Brentford on 9 January 2013, before re-signing for Maidenhead United on loan for the rest of the season on 21 February. Mawson was recalled from his loan early on 28 November after four appearances.
Luton Town (loan) On 28 November 2013, Mawson moved on loan to
Conference Premier club
Luton Town until 4 January 2014, to cover for injuries to
defenders Steve McNulty,
Andy Parry,
Alex Lacey and
Anthony Charles. He made his debut in a 5–0 away league victory over
Alfreton Town on 7 December, but was substituted for
Joe Davis at half time due to an injury. He returned to Brentford on 10 January after making just one appearance.
Welling United (loan) On 31 January 2014, Mawson joined Conference Premier club
Welling United on loan until the end of the
2013–14 season. He made his debut with a start in a 1–1 draw away to
Tamworth on 22 February. Mawson scored his first Wings goal on his second appearance, heading home the second in a 2–0 home win over
Gateshead on 25 February. A knee injury disrupted Mawson's time at Welling and he returned to Brentford at the end of the season, having made 9 appearances and scored one goal.
Wycombe Wanderers (loan) Mawson joined
League Two club
Wycombe Wanderers on 9 August 2014 on a one-month youth loan, as cover for the injured
Gary Doherty. He made his Wycombe debut (the first
Football League appearance of his career) on the opening day of the
2014–15 season, playing the full 90 minutes of a 2–0 away win over
Newport County alongside former Brentford teammate
Aaron Pierre at centre back. After appearing in each of Wycombe's first six matches of the season, Mawson's loan was extended until 1 January 2015. Mawson's 100% appearance record came to an end on his 19th appearance of the season, after suffering an injury in a 3–1 defeat to
Burton Albion on 17 November. His performance won him a place in the Football League Team of the Week. On 3 January 2015, Mawson's loan was extended until the end of the season, including the play-offs if required, with no recall clause. Mawson's three goals in four matches in March helped ensure Wycombe held onto the third automatic promotion place. He scored a vital winning goal in Wycombe's 2–1 victory over
Cheltenham Town on 11 April, to end a run of successive defeats, which kept Wycombe four points clear of fourth-place
Bury. Mawson's performance was recognised with his second inclusion of the season in the Football League Team of the Week. Mawson's 97th-minute winner in a 3–2 victory over
Northampton Town on the final day was not enough to prevent Wycombe from having to settle for fourth place and a
play-off semi-final matchup versus
Plymouth Argyle. However, his season ended in disappointment after a penalty shoot-out defeat to Southend United in the
final. He finished the 2014–15 season with 50 appearances and seven goals. He also won the Wycombe Wanderers Independent Supporters' Club Player of the Year award. He finished third in the running for the League Two Player of the Year award.
Barnsley Mawson signed for
League One club
Barnsley on 30 June 2015 on a three-year contract. He impressed in the
2015–16 season, scoring seven goals in 58 appearances. and in earning promotion to the Championship after beating Millwall 3–1 in the play-off final.
Swansea City in 2017 After just four league matches experience in the
Championship with Barnsley, Mawson signed for
Premier League club
Swansea City on 30 August 2016 on a four-year contract for an undisclosed fee. He made his full debut on 22 October 2016 in the 0–0 home draw against
Watford in the Premier League after which he presented with the man of the match award for his work in defence. He scored his first goal for the club on 3 January 2017 in a 2–1 win against
Crystal Palace. In the
2017–18 season, Mawson scored the only goal in a 1–0 home win against
Liverpool on 22 January 2018 to help Swansea's survival hopes. Despite this, the club struggled, particularly on the attacking point of view, and despite the player featuring in all 38 Premier League fixtures, he did not prevent the club's relegation, which was confirmed on the final day of the season.
Bristol City (loan) On 6 September 2020, Mawson signed for
Championship club
Bristol City on a season-long loan. On 26 March 2021, Mawson was recalled by
Fulham after making eleven league appearances for
Bristol City.
Wycombe Wanderers On 11 August 2022, Mawson re-signed for
League One club
Wycombe Wanderers, with whom he had previously been on loan, on a one-year deal. On 14 February 2023, Mawson retired from football due to injury. ==International career==