The Gabon international departs Stamford Bridge less than a year after initially being signed from Barcelona, the hope having been that he would solve Chelsea's issues in the final third.
However, Aubameyang's time in West London did not pan out as he would have hoped, his former Borussia Dortmund boss Thomas Tuchel being sacked within a week of his arrival.
The 34-year-old did prove effective for the Blues during Graham Potter's early weeks at Stamford Bridge, but he could not maintain his performances and ultimately dropped significantly down the pecking order.
As a result, Aubameyang netted just once in 15 Premier League appearances for Chelsea, a further two strikes and one assist coming from six outings in the Champions League.
While further details of the deal have not been disclosed by Chelsea, it has been alleged that owners Todd Boehly and Clearlake Capital were happy to hand Aubameyang a free transfer in order to get his wages off their outgoings.
The Premier League giants will be relieved to make greater strides into boosting their position with FFP, the onus now on finding a buyer for Romelu Lukaku.
Chelsea are hoping that either Juventus or a club in Saudi Arabia are willing to meet their demands for the Belgium international with head coach Mauricio Pochettino having already confirmed that he has no future at the club.
As many as 12 of last season's senior squad have now left Chelsea, and others will follow with Hakim Ziyech also out of Pochettino's plans despite a move to Al-Nassr falling through.
From Marseille's perspective, they have acquired the services of a player who had spells in French football with Dijon, Lille, Monaco and Saint-Etienne during his early days as a professional.
Between 2011 and 2013, Aubameyang netted 35 times from 73 outings for Saint-Etienne, earning him his switch to Dortmund which was then followed by a successful stint at Arsenal.
New head coach Marcelino Garcia Toral has now signed three players this summer, Aubameyang following the additions of Renan Lodi and Geoffrey Kondogbia.
Marseille have wanted to do a considerable part of their business for the summer as soon as possible due to their participation in the Champions League qualifying rounds.