The forward was hit with a four month suspension in September after walking out on Spartak.
He wanted to have his contract terminated, claiming Spartak were holding out on paying a bonus due to him.
A compromise could not be reached, prompting the Russian League to ban him until January 4.
He trained with Dinamo Kiev, who were keen to sign him, in order to keep his fitness levels up, but it was Marseille who were the most persuasive.
A deal has been struck and he will sign with the Stade Velodrome side for an undisclosed fee on January 1.
After agreeing on the details, Sychev said: "I'm satisfied with the offer and I'm also happy the conflict between myself and my former club is over."
Talk of a ‚é¼6 million move is wide of the mark, but Spartak are said to be happy with the compromise struck with Alain Perrin`s l`OM.
L`OM chief Perrin believes they have pulled off a notable transfer coup, saying: "To sign such a player is a great opportunity for us.
"He is a player who can boost our attack. He is fast, has great technique and is very intelligent."
Asked when Sychev will be ready, Perrin added: "Not straight away, but he will help us this season.
"At some point in January or February he will be ready.
"We want to utilise him as quickly as possible, however this allows us to adapt him into next season`s squad six months early.
"But I must stress that this is not the miracle solution to our attacking situation.
"I noticed him at the World Cup. Russia were eliminated early, but he made a good impression.
"To get a player of such potential is good for us, our financial situation means we cannot buy an established attacker."
