The 25 year-old who is yet to make his debut for the French national side will sign a four year-deal to join Marseille for a fee of around 4-5 million euros.
Alessandrini joins most likely due to the probable departure of Mathieu Valbuena who wants to experience another challenge before he ends his career and could go to either Spain or Italy at this point in time.
Alessandrini told the OM website this after his move. "I am very proud.
"Last year I could have come here, it did not happen and I am very happy to sign today.
"I thank the club, the president and the coach who made it happen.
He is also relishing the opportunity to play his home matches with the passionate crowds at the Velodrome.
"It is a good few years since I left Marseille (but) I know what it is like every weekend, especially at the Velodrome. It is something exceptional to have support like this."
Alessandrini made 27 League appearances last season with the pacy wide attacker scoring 6 goals and making 7 assists.