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.
29. Gary O’Neil - 193 appearances
O’Neil made his Pompey debut aged 16 and played just shy of 200 games for the club. The midfielder scored in successive home games during the ‘Great Escape’ of 2006 prior to leaving for Middlesbrough in 2007. Photo: PICTURE: WILL CADDY (HK04-26)
30. Ben Close - 190 appearances
Now plying his trade for Doncaster Rovers, Close initially signed a two-year scholarship with the Blues after progressing through the youth ranks. Close made his debut in an EFL Trophy victory against Yeovil, and left for Donny this summer. Photo: Jason Brown
31. Matt Taylor - 203 appearances
Signed in the summer prior to promotion to the Premier League, Taylor was a key asset for Pompey during the majority of his six-year stay. Wasn’t afraid of scoring remarkable goals either, with his 40-yard effort against Sunderland winning Goal of the Month. Photo: PICTURE:STEVE REID(071558-111)
32. Christian Burgess - 210 appearances
An instrumental part of the League Two title-winning team of 2017, Burgess also became a key member of the defence under Kenny Jackett. Alongside Enda Stevens, Burgess was named in the League Two Team of the Year in 2017 and, since leaving the club, has found success in Belgium. Photo: Robin Jones