Kolasinac, who had six months left on his Arsenal contract, has terminated his contract after reaching a mutual agreement with the club.
The 28-year-old has joined Olympique Marseille signing an 18-month contract until June 2023.
The Bosnian signed for the Gunners from Schalke in 2017 as a free agent, after a spectacular season at the German Club, which saw him make it to the Bundesliga Team of the Year for the 2016-2017 season.
He made an impressive start to his Arsenal career, scoring a goal in the FA Community Shield game against Chelsea, which ended 1-1 and the Gunners went on to win the match penalties.
The fullback made 118 appearances for the North London club, lifting the FA Cup once and the Community Shield twice. He spent the second half of last season on loan at Schalke, who were relegated from the German first division that season.
“Everyone at Arsenal would like to thank Sead for his contribution to the club since he joined us in 2017 and wish him all the best for his future.”, read the club’s website.