Their Academy have won the Youth Alliance Under-18 South East League title by beating Luton Town 4-2 over the weekend.
Jae Heon Kim grabbed a brace and Brandon Haunstrap and Conor Chaplin added to the goals for Andy Awford’s side.
Although Pompey ultimately finished a point behind Leyton Orient, their nearest title challengers, due to a late change in the set-up of the league they would work out the table on a points-per-game basis.
Orient played 21 games throughout the season while Portsmouth only 20, thus crowning the south coast side champions.
Portsmouth’s Academy coach Paul Hardyman told their official club website: “I’m really pleased for the lads because they’ve worked hard all season.
“A lot of things had to come together over the last few weeks for us to win the league, but we’ve done it.
“When we conceded so early, we began to wonder if it was going to be our day, but we then scored four really good goals to turn things around.
“Jae’s second goal in particular was fantastic and the goalkeeper had no chance of stopping it.
“Luton came at us in the second half and caused a few problems, but we stayed tight and only conceded one.
“The result was particularly pleasing because so many of our under-18 players were unavailable. We had a really young side out, but they did a great job.”