The move was announced by the Toffees on their official Twitter account on Wednesday, with the left-back signing a contract until 2023:
"Everton is a big club with a great history," he said in a statement on the club's official website. "I want to play games, win games and excite the fans with the quality of our football. I played good football in Rome and I played well, too, in Barcelona. I progressed a lot as a player and as a person by playing with the best players in the world."
Digne becomes the second signing made by new Everton boss Marco Silva following the arrival of Richarlison from Watford.
According to Phil Kirkbride of the Liverpool Echo, the Merseyside club have agreed an £18 million deal with the La Liga champions for Digne, although that may rise to £20 million due to add-ons.
The switch brings an end to two years at the Camp Nou for the 25-year-old, in which he struggled to force his way into the side at the expense of Jordi Alba. Barcelona posted the following clip of Digne reflecting on his time at the club:
Previously Digne had a spell with Roma on loan having struggled to cement a first-team place at Paris Saint-Germain.
Earlier in his career he had impressed at Lille, coming through the club's academy setup and forming an exciting partnership on the left flank with Eden Hazard. WhoScored.com broke down the attributes in his game:
Now the Frenchman needs some stability and regular football in order to rediscover the spark that was so evident early in his career.
Digne has the attributes to be a fine left-back for the Blues. Throughout his career he has showcased he has energy, tenacity and is intelligent enough to link up with attackers when he does overlap in the final third.
However, given he's been a fringe player at PSG and Barcelona, he hasn't had a consistent foundation upon which to showcase those talents regularly.
At Everton he will face some competition for his place in the team from veteran Leighton Baines. Ian Croll of the Liverpool Echo thinks the transfer is ideal given Baines will turn 34 in December:
Silva can at least be content he now has two quality options in the position and will hope Digne is able to strike up an understanding with new man Richarlison down the left flank.
Digne may not be the only man to trade the Camp Nou for Goodison Park this summer either. As noted by Kirkbride, Everton are also trying to wrap up a deal for Barcelona centre-back Yerry Mina.