Cornet, who can play either on the wing or at left-back, played 36 times in France's top flight last season, starting 29 games.
He contributed five assists – bettered by only Memphis Depay (12) and Karl Toko Ekambi (six) – and two goals as Lyon missed out on qualifying for the Champions League by two points.
💬 “I am excited to be joining Burnley in the Premier League and to play with and against many of the greatest players in the world."— Burnley FC (@BurnleyOfficial) August 29, 2021
👉 https://t.co/EZgqsr0ygk#WelcomeCornet🍦| #UTC pic.twitter.com/1wJfqVM73F
Cornet should add considerable productivity to Sean Dyche's attack, with only Dwight McNeil (five) having registered as many league assists as him last term out of Burnley players, while just three of the Clarets' squad – Ashley Westwood (34), Matthew Lowton (26) and McNeil (23) – created more goalscoring opportunities from open play than the Ivory Coast international's 22.
A regular since joining from Metz in 2015, the 24-year-old scored 51 times in total for Lyon, with one of those goals coming in an impressive 3-1 win over Manchester City in the 2019-20 Champions League quarter-final just over a year ago.
"I am excited to be joining Burnley in the Premier League and to play with and against many of the greatest players in the world," Cornet, who will wear the number 20, told Burnley's official website.
"I have developed the greatest respect for Burnley and what the club has done. I welcome the challenge of hard work and am fully committed to doing what I can to contribute. I look forward to what we can achieve."
Cornet represents the fourth senior addition of the transfer window for Burnley, who had already brought in Nathan Collins and Wayne Hennessey, while Aaron Lennon last week re-joined the club.