The Turkey midfielder will move back to his homeland on a four-year contract after spending two seasons in La Liga with the Mestalla outfit
The Istanbul club lost Emre Belozoglu to Atletico Madrid on a free transfer this summer, and have long been linked with a move for the fomer Galatasaray player to bolster their midfield options.
Since moving to Mestalla two years ago from Fener's city rivals, the 26-year-old failed to secure a regular starting berth for the Liga club, and said that he was looking forward to a change of scenery, and wanted to prove to the supporters that his Galatasaray days are behind him.
"I'm so excited and happy. There are no words to describe how big Fenerbahce are. I'm proud to be a part of this club," he told the club's official television channel.
"I want to show my gratitude to Fenerbahce fans. They haven't shown me any animosity. I will do everything to deserve this shirt. I will fight to be accepted by the fans."
The Turkey international has made 28 appearances for his country since making his debut four years ago, and was part of the team that reached the Euro 2008 semi-finals.