The former Burton Albion attacker became a centurion in the 4-0 victory over Sunderland, and even netted in the 4-0 win.
He now joins current team-mates Ronan Curtis, John Marquis, and Lee Brown in reaching the milestone.
Click through to see who else Harness joins in Pompey’s 21st century 100 club.
21. Jack Whatmough - 136 appearances
Like MacGillivray, Whatmough left the club this summer. After graduating from the academy in 2012, a series of serious injuries prevented him making more Pompey appearances. Scored a total of three goals for the club. Photo: Joe Pepler
22. Nigel Quashie - 163 appearances
Quashie spent five years at Fratton Park and helped the club reach the Premier League in 2003. The resulting season saw Quashie become a mainstay in the side that finished 13th in the league. The former Scotland international scored 14 goals for the club before following Harry Redknapp to Southampton in 2005. Photo: JPIMedia
23. Tom Naylor - 149 appearances
Former Blues captain Naylor was an integral member of Kenny Jackett’s squad. With 13 goals to his name at Pompey, perhaps his departure to Wigan in the summer was the most detrimental to the club. Photo: Jason Brown
24. Ronan Curtis - 154 appearances
The Republic of Ireland international has been key to the club’s attacking play since his arrival in 2018. That has attracted much interest in the Irishman, who remains at Fratton Park. Photo: Jason Brown