Roberto De Zerbi has signed a three-year deal to take over as Marseille head coach.
Marseille revealed earlier this week that an "agreement in principle" had been reached for the former Brighton boss and it has now been made official.
De Zerbi left the Seagulls at the conclusion of the 2023-24 campaign after a successful 20 months at the Premier League club, where he guided them into the Europa League for the first time.
"I'm delighted to be joining Olympique de Marseille, as I had a very strong desire to join the club," De Zerbi said.
"The history and prestige that surround OM, the passion and fervour of its supporters, and the seriousness and enthusiasm shown to me by Frank (McCourt), Pablo (Longoria) and Medhi (Benatia) were all decisive factors in my decision to embark on this exciting challenge.
"I can't wait to sit on the bench at the Orange Velodrome, this time as OM coach, and help the club regain the position that Marseille deserves."
Marseille endured a turbulent previous campaign and finished eighth in Ligue 1 after they went through three different permanent head coaches.
President Longoria added: "We are very proud to welcome Roberto to Olympique de Marseille, a talented coach with a European reputation.
"As well as being enthusiastic about the idea of coaching OM from the outset, he has all the qualities required to succeed on our bench.
"His decision to join us sends out a strong signal about the club and the new sporting cycle we are embarking on."