Marseille took the lead against Reims through Amine Harit, but goals from Sergio Akieme and Yaya Fofana put the visitors in front.
However, Greenwood secured a point for Marseille as he managed to find the net with a header.
It emerged this week that Greenwood, who has one senior cap for England, is set to switch his allegiance to Jamaica.
Mason Greenwood was on the scoresheet for Marseille in their 2-2 draw at home to Reims
Greenwood left United this summer to join Marseille in a £27million move.
He had a loan spell at Getafe last campaign in which he scored ten goals in 36 games across all competitions.
Greenwood didn't play for United again after being arrested in January 2022.
He was then charged with attempted rape, assault and controlling and coercive behaviour.
Greenwood vehemently denied any wrongdoing and the charges and case were dropped in February 2023 when key witnesses withdrew.
During his time at United, Greenwood made 129 appearances and scored 35 goals, while he provided 12 assists.