The veteran striker scored the only goal of the game just before the hour mark as HJK beat KuPS 1-0 at the Tammelan Stadion in Tampere to win the cup for a record-extending 15th time, yet their first since 2020.
Since that previous triumph, KuPS had won the cup in three of the four following editions, including last season, but their recent stranglehold on the competition was ended by Finland's historically most successful side.
The match itself was incredibly tight, with only one shot on target in the first half, and only one apiece in the second 45 minutes. However, it was the Helsinki side that took their second-half opportunity.
After patient build-up on the left, Alex Ring drove at the KuPS defence, getting a fortunate touch along the way as he reached the edge of the box, where he fed Aberdeen loanee Vicente Besuijen on the right side of the penalty area.
The Dutchman needed no second invitation to square the ball across goal to an unmarked Pukki, who applied the simplest of finishes for his 19th goal in all competitions since rejoining HJK at the start of the season.
That was enough for Miika Nuutinen's side to claim the trophy, which they lifted in front of a strong contingent of fans who had made the trip to Tampere.
Both sides will return to league action in midweek, with HJK now in search of a Veikkausliiga and Suomen Cup double, while KuPS are seeking to retain the trophy they still hold, having done the double in 2024.