Thomas Mark Harris (born 29 December 1998) is a Welsh professional footballer who plays for EFL Championship club Oxford United and the Wales national team.

[4][5] A series of illnesses and injuries throughout the Cardiff squad gave Harris the chance to make his Championship debut on 22 April, playing in a five-man midfield in a 0–0 draw at Wigan Athletic.

[11] After initially establishing himself in the first team, Harris suffered a concussion while on international duty and was unable to regain his place on his return because of the form of fellow forwards Jamille Matt and Pádraig Amond.

[14] He made three starts and three substitute appearances for the "Valiants" before being allowed to return to Cardiff early by manager John Askey after going five weeks without a first-team game.

[21] Harris came off the bench to make his first appearance of the 2020–21 Cardiff City season in a 3–2 defeat away at Queens Park Rangers on 31 October.

[24] Harris then faced stiff competition in the second half of the campaign after new manager Mick McCarthy signed Max Watters and used wingers Josh Murphy and Sheyi Ojo as strikers.

[26][27] Speaking in February, manager Steve Morison said that he was giving Harris a run in the starting eleven because of his impressive work in training and was rewarded as he scored his fourth goal of the campaign.

[34] Following a strong end to the season, scoring six goals in as many matches as Oxford secured their place in the play-offs, Harris was awarded the EFL League One Player of the Month for April 2024.

[38] Harris continued his form into the 2024–25 season, scoring four goals in his first four matches, being named EFL Championship Player of the Month for August.

[47] On 30 August 2021, Harris received his first call up to the senior squad as manager Rob Page sought replacements for the injured Aaron Ramsey, Joe Rodon, George Thomas and Neco Williams.

[48] He made his debut on 5 September, replacing clubmate Rubin Colwill in the 57th-minute of a 3–2 victory against Belarus in a 2022 FIFA World Cup qualification game.