Born in Cormeilles-en-Parisis, Val-d'Oise, Proment spent most of his career playing for FC Metz, making 261 appearances in six seasons, and SM Caen. After winning promotion from Ligue 2 with SM Caen, Proment signed a three-year deal with Antalyaspor in June 2010. However, he left the club after making only eight league appearances in January 2011. He came back to Caen, helping the team yo secure its position in Ligue 1. At the end of the season, in a surprising move, he goes back his first club FC Metz, which is in trouble, having been relegated for the first time of its history in Championnat National (third level). Gregory Proment explained that he felt that it was his duty to help his training club to come back to Ligue 2, despite a much lower salary, showing attachement and loyalty to the club he spend years with. This attitude, uncommon in modern football, makes him one of the most beloved players ever among Metz fans, who elected him in the team of the century. Proment's experience and leadership in a team of talentuous but young players proved essential. Metz finished second, and secured promotion to Ligue 2. Proment announced at the end of the season his retirement from professional playing, and went back to Caen, to held a coaching position with the reserve team.