The France international signed a five-year deal with the Premier League club.
Digne joined Barca from Paris St-Germain in 2016 and won La Liga and Ligue 1 titles with his former clubs.
He has 21 international caps for France and was on standby for the 2018 FIFA World Cup winners earlier this summer.
Speaking after signing for The Toffees, Digne said: “Everton is a big club with a great history. I want to play games, win games and excite the fans with the quality of our football.
“I want to show my best football here and discover the best league in the world. Everybody loves the Premier League. I am loving the fact I am coming here.
“I am not afraid, I am excited. For me, it is a new challenge to discover a country, a league, people and a great club such as Everton. It is fabulous.”