Mason moved to Hull City in 2016 for a club record fee, where he suffered a fractured skull in January 2017 in a match against Chelsea.

[4] He made his first-team debut in the group stages of the UEFA Cup on 27 November 2008, coming on as an added-time substitute for David Bentley in a 1–0 away win against Dutch club NEC.

[20] On 29 December 2011, Mason and teammate Harry Kane agreed a loan deal with Championship club Millwall from 1 January until the end of the season.

[21] Mason made an appearance in Tottenham's goalless draw in the Europa League group stages against Lazio at White Hart Lane on 20 September 2012, coming on as an added-time substitute for Mousa Dembélé.

[23] On the last day of the winter transfer window, Mason joined Ligue 1 club Lorient on loan for the remainder of the 2012–13 season, making his move out of England for the first time.

[25] On 23 July 2013, Mason signed on a season-long loan for League One Swindon Town,[26] joining fellow Tottenham players Massimo Luongo, Grant Hall and Alex Pritchard.

[28] After a successful pre-season in the United States with Spurs, Mason was included in Mauricio Pochettino's Premier League squad.

[29] On 24 September 2014, he made his first appearance of the season as well as scoring his first goal for Tottenham, an equaliser in a League Cup fixture against Nottingham Forest, which Spurs went on to win 3–1.

[29] On 2 November, against Aston Villa, Mason stuck his head in the chest of opponent Christian Benteke, who reacted by striking him with his hand.

[41] After a disappointing 2015–16 campaign with only eight league starts, Mason was bought by Hull City on 30 August 2016, for a fee believed to be around £13 million, a club record.

[44] On 22 January 2017, in a Premier League match against Chelsea, Mason suffered a fractured skull that required surgery after a clash of heads with defender Gary Cahill.

[56] On 23 March 2015, Mason received his first call up to the senior England team for a European qualifier against Lithuania and a friendly against Italy, after Adam Lallana withdrew due to injury.

[57] He made his debut in the latter match on the 31st, replacing Jordan Henderson for the last 16 minutes of a 1–1 draw at Juventus Stadium, assisting Andros Townsend's late equaliser.

[60] He was made the official academy coach for the Under-19 UEFA Youth League side in July 2019,[61][62] and then the head of player development (U-17 to U-23) in August 2020.

[64] At the age of 29, he became the youngest manager of a Premier League team; the previous record holder Attilio Lombardo of Crystal Palace was 32.

[70][71] During Conte's health-related absences in February 2023, Mason worked closely alongside assistant head coach Cristian Stellini in the Tottenham dugout.