British media reported that Chelsea had terminated Aubameyang's contract, which had one year to run, following a disappointing spell with the West London side.
The striker made just five Premier League starts, netting once against Crystal Palace in October.
He also scored twice in the Champions League group stage but was then left out of Chelsea's squad for the knockout stages.
"We would like to thank Pierre and wish him well as he begins the next chapter of his career," Chelsea said in a short statement.
The French-born striker returns to France 10 years after his stint at St Etienne, where he spent three seasons from 2010-2013.
Aubameyang also played for Ligue 1 clubs Lille and AS Monaco early in his career before having successful spells with Borussia Dortmund and Arsenal.
He is Gabon's record scorer with 30 goals in 73 matches and was named the African Footballer of the Year in 2015.
He retired from international soccer in 2022 but announced his return to the Gabon team this year.
