The Ivory Coast international put pen to paper on a deal with the north London side following weeks of speculation linking Pepe with a move to Arsenal.
The new club-record signing will wear the number 19 shirt at the north London side after becoming the fourth arrival of a busy summer transfer window for Emery.
The Arsenal manager was quick to talk up the significance of Pepe’s arrival after the Gunners won the competitive race for the Ivorian’s signature.
“Nicolas is a highly-rated and talented winger who was wanted by many of the top teams in Europe,” Emery told Arsenal’s website.
“Signing a top-class winger has been one of our key objectives in this transfer window and I’m delighted he’s joining.
“He will add pace, power and creativity, with the aim of bringing more goals to our team.”
The Gunners have been the busiest of the top-six clubs in the transfer window after signing Pepe, Gabriel Martinelli, William Saliba and Dani Ceballos.
Arsenal will start the Premier League season with a clash against Newcastle United at St James’ Park on Sunday 11 August.
The north London side will be hoping to finish in the top four for the first time in four seasons.
Arsenal narrowly missed out last term after Emery’s side finished behind Chelsea FC and Tottenham Hotspur.
The Gunners lost 4-1 to Chelsea FC in the Europa League final to end Emery’s first season without a trophy.
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