Lewis John O'Brien (born 14 October 1998) is an English professional footballer who plays as a midfielder for EFL Championship side Swansea City on loan from Premier League club Nottingham Forest.

Born in Colchester,[3] O'Brien began his career with Huddersfield Town at the age of 11,[4] where he was named Academy Player of the Year for the 2017–18 season.

[14] Later that month, journalist Simon Parker said that O'Brien was "enjoying an outstanding first season in senior football" and was "a driving force in City's push to get out of the League One drop zone".

[21][22] In February 2019, following a poor run of results which saw the club drop into the relegation zone, O'Brien spoke about his confidence in the players turning things around.

[9] In March 2019 new manager Gary Bowyer rested O'Brien from first-team duties, ending "a run of 30 successive league starts" in order to be fully fit for the club's relegation battle.

[9] In July 2019, following the end of his loan spell with Bradford and upon his return to parent club Huddersfield, O'Brien was given an improved three-year contract.

[42][43] On 30 July 2024, O'Brien returned to Major League Soccer to join Los Angeles FC on loan for the remainder of the 2024 season, with a purchase option.