The clubs have agreed a two-and-a-half-season loan deal for the 30-year-old Turkey midfielder, who has struggled to hold down a regular first-team place since moving to Barcelona in 2015.
Basaksehir president Goksel Gumusdag said: "Arda is returning to his country wearing the orange kit.
"This is not just a transfer for Basaksehir, but a transfer for Turkey."
Barcelona announced the signing of Turan from Atletico Madrid for an initial fee of £24m in July 2015 but, because of their 14-month ban on registering new players, he could not make his debut until the start of 2016.
He won six trophies during his time at the Nou Camp, but only made 55 appearances and scored 15 goals
