The 26 year-old French international joins the North London side on five-year deal, breaking the previous amount spent on Mesut Özil from Real Madrid back on transfer deadline day in September 2013, when the Gunners paid £42.5 million for the German.
Lacazatte is Arsene Wenger's second signing so far this summer, after full-back Sead Kolasinac joined on a free transfer from Bundesliga side Schalke 04.
The Frenchman will now fly out with the squad this weekend for a four-match pre-season tour of Australia and China.
Wenger's signal of intent
After manager the much maligned Wenger signed a new two-year deal at the Emirates at the conclusion of last season, fans have been clamouring for both he and owner Stan Kroenke to finally loosen the club's notoriously tight purse strings ahead of the new season.
The addition of Alexandre Lacazette appears to be the first sign of change in N5, with reports of multi-million pound moves for AS Monaco frontmen Thomas Lemar and Kylian Mbappe refusing to disappear - despite Arsenal failing to qualify for the Champions League for the first time in 18 years.
Since the departure and waning days of Thierry Henry, Arsenal have lacked an out and out goal scorer that has all the tools; both pace and a killer instinct in front of goal.
Olivier Giroud's 69 goals in 164 appearances have shown glimpses that the former Montpellier number 10 has the ability to be that man however the striker's wasteful ways, have tended to dog his otherwise sterling five plus seasons at the club.
Robin van Persie never showed the Gunners his best due to injury. Having missed out on the likes of Gonzalo Higuain and Luis Suarez in past years, is Lacazette the solution fans have been craving?
Crafted in the guise of the Gunners former club legend Henry as a winger, since replacing Les Gones' iconic Argentine forward Lisandro López in 2013 as a forward, Lacazette has scored 129 in four seasons France, having never scored less than 22 in a single campaign.
As the sagas of Alexis Sanchez and Ozil continue to rumble on and with further additions yet to come, Lacazette is set to spearhead a more natural pacier attacking line in the coming season for Arsenal, with the aim of firing the club back up the table.
The only remaining questions left to answer now are, as to which personnel that will consist of.