The Brazilian center-back who made 34 appearances in all competitions last season as Les Dogues finished fourth in Ligue 1.
Gabriel has been linked with a move to Manchester United, Everton, and Serie A club Napoli before joining Arsenal.
Gunners confirmed the signing on the club website and social media on a long-term contract.
— Arsenal (@Arsenal) September 1, 2020
Gabriel is the second player to join Arsenal from Lille in the past 12 months, following Ivory Coast international Nicolas Pepe’s move to the Emirates for a club-record £72m last summer.
Pablo Mari and Cedric Soares made their loan moves permanent from Flamengo and Southampton respectively earlier this summer.