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.
1. A new chapter
Former New York City winger Harrison joined the Whites on a season-long loan from Manchester City in July 2018 having spent the second half of the previous season on loan at Middlesbrough. Picture by LUFC.
2. Whites debut
Harrison's debut came as an 89th-minute substitute for Gjanni Alioski in United's season opener at home to Stoke City in August 2018 in which the Whites recorded a 3-1 victory in Marcelo Bielsa's first game in charge. Picture by Tony Johnson.
3. Full debut
After coming on as an 89th-minute substitute in United's Championship opener at home to Stoke, Harrison's full debut came in the Carabao Cup clash against visiting Bolton Wanderers nine days later. Photo by Bruce Rollinson.
4. Full league debut
Harrison's first league start for Leeds then came in the goalless draw at home to his former club Middlesbrough on the last day of August 2018. Picture by Tim Goode/PA Wire.
5. First goal
Harrison's first goal for Leeds came in the very next game as the City loanee struck in the 88th minute from outside the box to seal the Whites a 1-1 draw at Millwall in September 2018. Picture by James Hardisty.
6. Jubilation
Harrison races away to celebrate his first goal for Leeds in the 1-1 draw at Millwall as Pontus Jansson smiles looking on. Harrison played in a very central attacking role. Picture by James Hardisty.