Born in Parisian suburb Chartreux, Alessandrini spent six years in the club's youth set-up before leaving for Gueugnon in 2005.
He came up through the leagues with Clermont and then Rennes before finally returning to his roots after OM sealed his signing on Wednesday for a reported 5million euros.
The move almost happened last summer but Rennes were reluctant to let him leave after helping him through the recovery process following a knee ligament injury.
Having finally got his wish, he told OM's website: "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."
The 25-year-old is relishing the opportunity to play in front of the passionate crowds at the Stade Velodrome.
"It is a good few years since I left Marseille (but) I know what it is like every weekend, especially at the Velodrome," he said. "It is something exceptional to have support like this.
"I can't wait to see what happens, we have big objectives for this season. It's a big club, I will do all I can and give them the best possible."