The former England under-21s winger joined the club on loan from Manchester City back in July 2018 and is now on his third season-long loan from Pep Guardiola's side.
Those 100 games have produced 11 goals and the YEP's Lee Sobot picked out a handful of pictures telling the story of the now 24-year-old winger's Whites career so far.
13. Christmas miracle
Harrison also struck to put Leeds 2-0 up in a crazy game at Birmingham City that ended the club's fixtures of 2019 in which United sealed a remarkable 5-4 victory. Picture by Tim Goode/PA Wire.
14. One that got away
Leeds and Harrison got a taste of the big time in January's FA Cup tie at Arsenal and dominated the first half but ultimately fell to a 1-0 defeat. Photo by Shaun Botterill/Getty Images.
15. Unprecedented times
After a 15-week pause to the season due to coronavirus, Leeds returned to empty stadiums with Harrison netting in front of the Whites 'crowdies' at Elland Road in June's 3-0 win against Fulham. Photo by Martin Rickett/PA Wire.
16. We've done it!
After a storming end to the season, Harrison and Bielsa's Whites were then able to celebrate promotion at the second time of asking and in the ultimate style as Championship champions. Picture by Martin Rickett/PA Wire.
17. We are Premier League
Harrison then returned to Leeds on a third season-long loan and made an immediate impact on his first Premier League start by netting a superb goal at Liverpool in a 4-3 thriller. Photo by John Powell/Liverpool FC via Getty Images.
18. Scorcher
Harrison celebrates his fantastic strike against Liverpool with Helder Costa, left, and Patrick Bamford. Photo by SHAUN BOTTERILL/POOL/AFP via Getty Images.