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.
25. David James - 158 appearances
A bonafide Pompey legend, James produced a number of memorable moments for Blues fans. In 2007, he was named Player of the Year at the end of the campaign that saw him set a new top-flight clean sheet record. Prevented Pompey’s goal from being breached in the FA Cup final triumph over Cardiff. Photo: Chris Ison
26. Richard Hughes - 165 appearances
Despite not making the squad for the FA Cup final, Hughes was a member of the team that lifted the trophy due his appearances in the earlier rounds. Perhaps his finest moment for the club was scoring the winner in a 2004 FA Cup victory over Liverpool. Photo: PICTURE:STEVE REID(075168-27)
27. Nwankwo Kanu - 168 appearances
Pompey’s FA Cup final hero, Kanu scored the only goal of the game against Cardiff. The former Arsenal striker also scored in the 2-2 draw with AC Milan. He eventually left the club in 2012 after six years and 28 goals. Photo: Barry Zee
28. Matt Clarke - 175 appearances
Clarke was a member of the squad that lifted the EFL Trophy in 2019 and was a mainstay in Kenny Jackett’s side prior to his departure to Brighton. However, he’s yet to make a Seagulls appearance following two loan moves to Derby and West Brom, respectively. Photo: Joe Pepler