Milan Mandaric has resigned as Portsmouth chairman.
Gaydamak (left) will take up the reins from Mandaric
The Serb-American, who has been non-executive chairman since selling Pompey to Alexandre Gaydamak, will step down after Monday's game with Bolton.
Mandaric brought Pompey out of administration when he took over in 1998, and within four years took them into the Premiership.
He told Pompey's website: "I'll leave immensely satisfied and happy about what I have achieved."
Mandaric will make what is certain to be an emotional curtain call at Fratton Park at Monday.
He added: "I'm happy about whose hands I leave this club in.
"Alexandre Gaydamak has already made his own impressive mark on the club, which I fully expected and applaud.
"I am and always will be immensely grateful to the city which graciously bestowed upon me its freedom and our wonderful supporters whose relationship with me has no equal."
Mandaric insists he will maintain his ties with the club.
He said: "I will always be just a phone call away and will happily advise and help should the club need.
"I also hope to come back to matches as often as possible so in that sense it is no goodbye, but merely au revoir."
Mandaric was recently linked to a possible take over at Wolves, but he denied he wanted to get involved.