The 26-year-old underwent a medical at London Colney training ground on Tuesday and is expected to sign a five-year contract for a club-record fee, eclipsing the £42.5m paid to Real Madrid to sign Mesut Ozil in 2013.
With hopes of signing Monaco's Kylian Mbappe - a Real Madrid and Paris Saint-Germain target - fading, Arsenal manager Arsene Wenger managed to convince another of Ligue 1's star forwards to play at the Emirates Stadium.
Lyon club president Jean-Michel Aulas, who sanctioned the transfer on Sunday, has previously said the Premier League side must part with €65m to prise Lacazette away from Parc Olympique Lyonnais and the newly agreed deal includes bonuses worth £6m.
France international Lacazette was close to joining Atletico Madrid before the Spanish club's transfer ban was upheld and Aulas confirmed via French news outlet Le Progres that Wenger's side that the move is closer to €50m (£44m/$57m) rather than an "unrealistic" €65m (£57m/$74m).
Lacazette scored over 20 Ligue 1 goals in each of his last three seasons for Lyon and will become one of Arsenal's highest earners alongside Mesut Ozil, Alexis Sanchez and Theo Walcott.
The Gunners still hope to keep West Ham target Olivier Giroud , although they are prepared to let Lucas Perez, who joined last August but scored only once in 11 Premier League matches, leave the north London club this summer.
Arsenal also remain hopeful of a deal for Monaco's Thomas Lemar as well, but the youngster does not appear ready to force a move to the Gunners.
Leicester City winger Riyad Mahrez also remains a target of Wenger's after personally speaking to the 67-year-old on the phone over a fortnight ago.