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.
1. Marcus Harness - 100 appearances
The latest Pompey player to reach 100 appearances. The former Burton ace has impressed in recent weeks while operating behind two strikers in Danny Cowley’s 3-5-2 formation. Photo: Jason Brown
2. Glen Johnson - 100 appearances
A fans' favourite at Fratton Park, Glen Johnson enjoyed three successful seasons for Pompey. Most notably , he lifted the FA Cup in 2008, and who could forget that goal against Hull City? Photo: WILL CADDY
3. Shaka Hislop - 100 appearances
Hislop joined the Blues in 2002 and played an instrumental role in gaining promotion to the Premier League. The former West Ham and Newcastle goalkeeper kept his place in the team for the following two seasons in the top flight. Photo: Steve Reid
4. Niko Kranjcar - 100 appearances
The former Croatia international forged a great career on the south coast after arriving in 2006. An FA Cup winner in 2008, the now 37-year-old was technically gifted with both feet and scored a total of 12 goals in royal blue. Photo: Steve Reid