The former Plymouth Argyle midfielder left the aest London club in July after being deemed surplus to requirements and has now joined Michael Appleton's side on a one-month deal
The 30-year-old, who made 102 appearances for the Rs, scoring 17 goals, has signed a short-term contract, which could be extended depending on his performances while at the cash-strapped South Coast club.
Portsmouth have pulled off what could be described as a coup, with Championship sides Nottingham Forest and Bristol City known to be keen admirers of the Hungarian, and Pompey manager Michael Appleton has expressed his delight at signing a player of his calibre.
He told BBC Radio Solent: "He is a midfield player with bags of ability, he has got a good first touch and his passing is very good.
"Akos was playing Premier League football last season, but he's here because he wants to play football.
"It's quite a coup, I know his agent quite well and he was keen to come and play for the football club."
Appleton could not hide his frustration at being limited to a squad of just 20 players, with the 36-year-old hinting that other players wanted to join the League One outfit.
He added: "This is the type of player we can sign and with a little bit of backing the type of player we will continue to sign.
"We are now up to our 20 player limit as we are in administration which is annoying because there are other players like Akos Buzsaky who want to sign for the club."