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.
7. Match winner
After netting in the wins against Derby County and Swansea City at the turn of the year, Harrison bagged the only goal of the game in the 1-0 triumph at home to Sheffield Wednesday in April 2019. Picture by Tony Johnson.
8. Cruel end
Harrison's first season at Leeds ultimately ended in heartache with defeat to Derby County in the play-offs semi-finals, despite his brilliant assist for Kemar Roofe's goal in the first leg victory at Pride Park. Picture by Tony Johnson.
9. Back with a bang
Harrison then re-joined Leeds on a second season-long loan in July 2019 and netted United's third and final goal in the season opening 3-1 victory at Bristol City with Bielsa also back for a second year. Picture by Mark Kerton/PA Wire.
10. Sore one
Harrison was left to reflect on a night of hurt after missing United's final spot kick in the 5-4 defeat on penalties to Stoke City in the August 2019 Carabao Cup clash at Elland Road with Kalvin Phillips leading the consoling. Picture by Bruce Rollinson.
11. Flying
One of the best pictures of Harrison's time at Leeds came after his strike eight minutes from time to seal a 2-0 victory at home to QPR in November 2019. Picture by Simon Hulme.
12. Saviour
On a miserable, wet night in Reading, Harrison popped up at the far post to head home an 87th-minute winner to seal Leeds a 1-0 triumph in November 2019 as part of a month in which he was nominated for the player of the month award. Picture by Bruce Rollinson.