Mathieu Debuchy put pen to paper on a three-year contract with Saint-Etienne on Monday.
Former France right-back Debuchy joined Saint-Etienne on a free transfer from Arsenal in January, agreeing a deal for the remainder of the 2017-18 season.
The 32-year-old made 15 appearances as ASSE finished seventh in Ligue 1, scoring four goals to earn a prolonged stay at Stade Geoffroy-Guichard.
"I have really enjoyed these four months with Saint-Etienne," said Debuchy in a statement.
"Playing at home in such an atmosphere with the good results we have achieved in recent months reinforced my choice to extend with ASSE.
"The presence of [head coach] Jean-Louis Gasset also played a role in my decision."
Saint-Etienne's Ligue 1 rivals Toulouse announced the return of Alain Casanova as head coach.
Casanova, who spent three years with the club as a player and was in charge between 2008 and 2015, replaces Mickael Debeve at the helm.
Toulouse, who defeated Ajaccio in the relegation play-off in 2017-18 to remain in Ligue 1, announced the permanent signing of Max Gradel from Bournemouth.
