Matthew Sean O'Riley (born 21 November 2000) is a professional footballer who plays as a central midfielder for Premier League club Brighton & Hove Albion.

[5] Over the next two seasons O'Riley featured for the club's U21 side in several EFL Trophy group matches whilst on the fringes of the first team.

[7] On 24 January 2021, O'Riley signed for League One club Milton Keynes Dons, having spent six months training with the side as a free agent since leaving Fulham.

[8] Just a week after joining the club, O'Riley scored his first professional career goal in a 2–0 away win over AFC Wimbledon on 30 January 2021.

[20] On 26 August 2024, O'Riley joined Premier League club Brighton & Hove Albion for a fee of £25 million, signing a contract until June 2029.

[21] He made his debut the next day, starting in a EFL Cup tie against Crawley Town, but after a nasty tackle was injured nine minutes into the game and forced to come off.

[22] O'Riley subsequently underwent ankle surgery, with Brighton chairman Tony Bloom confirming that it was hoped he would return to full fitness "at some point in the latter part of the year.

[25] In February 2022, O'Riley declared his interest in representing Denmark internationally when he stated that: "I played for England youth teams but at the same time, I do feel quite Danish.

[28][29] On 20 November 2023, O'Riley received his first senior cap for Denmark, starting in a UEFA Euro 2024 qualifying match versus Northern Ireland.