The feat meant the 24-year-old - who had come short of lifting a major honour in 2016 when Real Madrid defeated Los Rojiblancos in the final of the Champions League - has claimed his first trophy in his professional career.
Striker Antoine Griezmann started the onslaught in the 21st minute after benefitting from a mistake by Marseille's defence.
Barely after the restart, the French outfit who had talismanic captain Dimitri Payet limp off in the first half were down to two goals with Griezmann, again, causing the damage.
The striker lobbed a nice effort past goalkeeper Steve Mandanda to double their lead, before Gabi sealed the win with a low drive at the death.
Partey came on as a late substitute to make his eighth appearance in the competition. He chalked up 477 minutes and contributed an assist.