The 30-year-old is a long-standing target of Cottagers manager Martin Jol, who has previously been frustrated in his attempts to land the player.
A dispute with Ukrainian club Dnipro prevented Boateng making the move to west London earlier this season.
The former Getafe, Cologne and Beitar Jerusalem ace posted a photo of himself holding a Fulham shirt at the club's Motspur Park training ground on a social network site.
Boateng said: "I'm finally happy."
"I have signed a two-year deal with Fulham FC. I'm happy to see this deal confirmed. Thanks God, my family and everyone who support me."
Fulham have yet to officially confirm the move.