Luke Terry O'Nien (born 21 November 1994) is an English professional footballer who plays as a defensive midfielder or centre-back and captains EFL Championship club Sunderland.

[4] Having signed his first professional contract at Vicarage Road in July 2013,[5] he was then called up by the first team to the pre-season friendly tour in Italy after he impressed staff during training.

[9] On 27 March 2014, O'Nien signed a one-month loan deal with Isthmian League Premier Division side Wealdstone.

[10] He made his debut as a late substitute in a win over Billericay Town on 31 March 2014, while his first start came three days later on 3 April 2014 in a 3–0 success over East Thurrock United.

[15] On 25 July 2015, O'Nien signed for League Two side Wycombe Wanderers on a one-year deal, having had a successful trial with the club.

[18] In his first season at Sunderland, O'Nien got attacked by a Portsmouth fan at Fratton Park after he got accidentally pushed into the stands by a player on the opposing team.

[27] Owing to his ancestries, O'Nien is eligible to play international football for either the England or Singapore national teams.