The 28-year-old has signed a four-year deal with Eusebio Di Francesco's side, bringing an end to his long association with Lyon, where he came through the youth ranks and made his first-team debut in 2009.
"After speaking with [sporting director] Monchi and the coach about their ambitions, I did not hesitate for a moment," said Gonalons, who has won seven France caps.
"For this reason there were no issues and everything was agreed very quickly.
"I cannot wait for this new adventure."
Gonalons' arrival adds to the signings of Rick Karsdorp, Hector Moreno and Lorenzo Pellegrini under new sporting director Monchi.
The club have, however, seen Mohamed Salah depart for Liverpool, while Leandro Paredes has joined Zenit.