An agreement has been reached following several days of negotiations between the two clubs.
The transfer is worth €25million including bonuses, according to Foot Mercato.
Sochaux, Mayenda's first professional club, will receive 20% of any future profit on the deal.
Mayenda becomes the fifth new arrival at Rennes this summer, following Adrien Thomasson, Issa Soumaré, Gonçalo Oliveira and Nicolas Lemaitre.
The 21-year-old will make his return to French football three years after leaving Sochaux for Sunderland.
Mayenda made his professional debut for Sochaux in December 2021, becoming the club's youngest ever player in a competitive match at 16 years and seven months old.
He joined Sunderland in July 2023 and spent part of the 2023-24 season on loan at Hibernian in Scotland before returning to the Stadium of Light.
The striker has made 45 appearances in the Championship for Sunderland, scoring eight goals and providing five assists.
He scored on his Premier League debut for Sunderland last season, netting the opener in a 3-0 win over West Ham United.
Increased competition for places in the Premier League limited Mayenda's opportunities, despite some promising performances from the bench.
Rennes will be hoping the move offers Mayenda the regular first-team football that proved harder to come by in England.