Umtiti ended his seven-year stay with Barcelona at the start of this month when his contract with the Blaugrana was terminated.
The 29-year-old's contract with Xavi Hernandez's side still had three years to run but he had effectively played a fringe role at the Camp Nou in recent seasons following a series of serious knee injuries.
Umtiti spent last season on loan in Serie A with Lecce, where he made 25 appearances.
Despite staying fit for much of last season there was no chance for Umtiti to reclaim a place in the Barcelona side and he has chosen to return to France.
He won two La Liga titles and the Copa del Rey on three occasions during his time at Barcelona after joining from Olympique Lyon in 2016.
Umtiti won the FIFA World Cup with France in 2018, scoring the only goal against Belgium in the semi-finals.
"Returning to France, logically I thought of Lyon but in the end I chose to go to a club that wanted me," Umtiti said.
"I have already tasted the France team, experienced exceptional moments, obviously these are things that I want to relive," he added as he aims to add to his 31 caps for Les Bleus.
