A product of their youth academy, the Frenchman moved back to the club after a five-year stint at Arsenal, leaving on a free transfer upon the expiration on his contract.
Prior to his move to England, the forward scored 129 goals in 275 games, earning Lyon a club-record £52m in the summer of 2017.
Capped 16 times by France, the bulk of his international appearances came while he was plying his trade in Ligue 1 and he rejoins a Lyon side who finished eighth last season on a three-year contract.
During his first spell at the club, Lacazette lifted both the Coupe de France and Trophee des Champions.
Arsenal boss Mikel Arteta hailed Lacazette as a “real leader” upon his departure and the stirker is looking to take those skills into helping restore former glories at the Groupama Stadium.
“Even without a European Cup to play, the project was more important than anything else,” Lacazette said.
“I felt I could be useful in the dressing room and on the pitch, it was the best decision. It is moving to come back. I want to help the club to return to the top and qualify for Europe.”