The 30-year-old Turan, inked final terms with the fast-rising Turkish league leaders after joining Basaksehir on a two-and-a-half-year loan deal from Barcelona.
"I am very excited by the idea of doing what I like to do most in the world. I have missed football a lot," Turan told reporters in Istanbul at his signing ceremony.
He joined Barcelona in 2015 after four successful seasons with Atletico Madrid but has been unable to hold down a first-team place.
With Turan receiving an annual salary of around eight million euros, according to Spanish media, the Catalan club were keen to offload him.
Basaksehir's chairman Goksel Gumusdag said Turan will, excluding bonuses, have a salary of 2 million euros until the end of this season and 4 million euros for next season, excluding bonuses.
Meanwhile, over the duration of the loan period, Barcelona has the right to sell the player to another club.
Were he to be sold next year, Basaksehir would receive 20 percent of the sale price and the year after it would receive 25 percent, Gumusdag said.
25% owners of Turan
"In other words we have become the 25 percent owners of Arda Turan without having to pay anything," added Gumusdag, a key figure in Turkish football who is married to the niece of President Recep Tayyip Erdogan's wife Emine.
Basaksehir have risen rapidly over the last two seasons to rival the established Istanbul triumvirate of Besiktas, Fenerbahce and Galatasaray.
With Turan joining international stars like Togo striker Emmanuel Adebayor and France's Gael Clichy, Basaksehir are serious title contenders, topping the table one point ahead of Galatasaray.