The 20-year-old Belgian-born midfielder impressed in Ligue 2 last season as he helped Guingamp earn promotion to the French top flight.
He made 34 appearances in the club's successful season, scoring two goals as they finished runners-up in the second tier.
Imbula has been a senior player with Guingamp since 2009 after splitting his youth career between a number of clubs, including current Ligue 1 champions Paris Saint-Germain.
Following his call up to the French Under-21 side earlier this year, he played four times in the Toulon Tournament, scoring one goal in the side's 4-1 thrashing of the United States.
And such showings have clearly convinced Marseille he is capable of playing at the top level, as a statement posted on the club's official website on Thursday revealed he is on his way to the Stade Velodrome.
"OM and Guingamp, through their presidents, have reached an agreement for the transfer of Gianelli Imbula, subject to successfully passing the medical examination and therefore the actual signing of the player's contract with Marseille," it read.
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