Kakuta still has three years left on his contract with the Blues, but is keen on regular first-team football.
The 21-year-old told L'Equipe: "Chelsea's sporting director Michael Emenalo told me (in July) it will depend on the coach's choices. I explained I would wait to see how it goes in pre-season.
"My decision is definite now. It is an important moment in my career. It is better for me to leave the club and find one where I could play matches regularly.
"Chelsea told me they rely on me. It is nice to rely on me, but I am 21-years-old. You can tell me that at 17-years-old or 18-years-old, but I need to play. I thought more players would have left the club."
"Stepping back, I believe Ligue 1 will be good for me," he added. "It will be a good stay. My objective is to play a complete season with 25 matches.
"Marseille is a club I like. In France, they are one of the three clubs I am following the most with Lyon and Lille. With the players they have, I have no concerns. The club is not finished."