The deal could rise by an extra £3 million in bonuses to the German club, who will see their number one join the Gunners on a five year deal.
Leno has spent 5 seasons with Leverkeusen, making over 300 appearances for the club. However, he has been on the edges of the German national team and despite being part of their Confederation's Cup winning-team in 2017, he was not selected for Jachim Lowe's World Cup squad.
This transfer calls in to doubt the future of veteran Arsenal goalkeeper Petr Cech, who has just one year left on his current deal at the Emirates and is expected to be replaced as the club's starting 'keeper next season.
Unai Emery has been quick to make additions to his new team's squad ahead of the new Premier League season, having already signed Stephan Lichtsteiner from Juventus and being close to confirming the transfers of Borussia Dortmund's Sokratis Papastathopoulos and Sampdoria's Lucas Torreira.