Financial terms were not disclosed but British media reported Brighton agreed on a deal worth 17 million pounds for Jahanbakhsh, eclipsing the 14 million pounds paid for forward Jurgen Locadia to PSV Eindhoven in January.
"Ali is a player that we have been aware of and monitored for a few years, and his versatility will increase our attacking options within the squad," Brighton manager Chris Hughton said in a statement.
"He can play in a wide position or central midfield attacking role, and I am now very much looking forward to working with him."
Jahanbakhsh was the highest scorer in the Dutch Eredivisie last season, netting 21 goals in 33 appearances for Alkmaar.
He has 41 caps for Iran and featured in all three of the country's group stage matches at the World Cup in Russia.
(Reporting by Hardik Vyas in Bengaluru; Editing by Andrew Bolton)
