The transfer had been heavily mooted and Pepe was clearly in boisterous mood after finally putting pen to paper.
He went on Instagram and put up a picture of himself in an Arsenal shirt, saluting with the words "@aubemeyang97 @lacazettealex Where are u?"
Arsenal confirmed the paperwork for the move, which is "subject to the completion of regulatory processes" had been finalised on Thursday, and Pepe would wear the No 19 shirt. The length of the deal was not announced, but is believed to be for five years.
Gunners head coach Unai Emery said: "Nicolas is a highly-rated and talented winger who was wanted by many of the top teams in Europe.
Who finishes where in 2019-20?
"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."
Pepe scored 22 Ligue 1 goals last season and was linked with a host of clubs over the summer including Manchester United and Napoli.