Defender James Bolton has joined the Blues on a three-year deal from Shrewsbury Town.
The 24-year-old will officially become a Blues player on July 1 when his contract with the Shrews expires.
On his move to Fratton Park, Bolton said: "There’s been interest for a while, so it was always at the back of my mind that I could be coming here.
"This is a massive club. I think there were other teams interested, but I look at where Pompey can go and that excites me.
"I’ve moved up gradually throughout my career, so I’ve got to embrace this opportunity and try to do well here.
"We should definitely be fighting for promotion and know that anything else isn’t acceptable for this club."