The Mali international made just 24 appearances for the Premier League outfit following his arrival in 2013
The Mali international made just 24 appearances for Villa following a move from Clermont in January 2013.
The defensive midfielder spent last season on loan with Kayseri Erciyesspor in the Turkish Super Lig and has now become the latest player to depart Villa Park, as Tim Sherwood oversees a close-season clear-out after the club's 17th-placed finish in the Premier League.
Darren Bent and Andreas Weimann have each left Villa for Derby County, while full-back Matthew Lowton is reportedly on the verge of signing for Burnley.
Having sealed a return to France, Sylla told Rennes' official website: "I needed to regain stability.
"The club is ambitious, the project is one that suited me the most.
"I want to achieve great things with Stade Rennais FC."
Rennes finished ninth in Ligue 1 last season under Philippe Montanier.