In a tweet with the hashtag, #YuvanaHosgeldinArda meaning "Welcome home Arda", the team shared a video with archive footage of Turan playing for Galatasaray.
Turkish media reported the new deal was for one year with an optional second year.
He was on loan to Istanbul Basaksehir from January 2018 in a one-and-a-half year deal, which ended in January after he wanted "to leave to write a new chapter in his career", the club said at the time.
Turan, 33, had played for Galatasaray between 2005 and 2011 before he left to play for Atletico Madrid. He then joined Barcelona in 2015.
One of Turkey's best-known sportsmen and a staunch supporter of Turkish President Recep Tayyip Erdogan, Turan has received wide attention for his disciplinary record.
The midfielder was given a 16-match suspension after shoving and verbally abusing a referee in May 2018
A court gave him a suspended sentence of almost three years last year over a brawl involving a famous singer at a nightclub in Istanbul.