The 24-year-old has signed a four-year contract at Goodison Park and passed a medical on Saturday, the Premier League club confirmed on their website. His signing was completed too late to feature in Monday's clash with Manchester United but he will be unveiled to the home fans at the game.
Mirallas, who has been handed the number 11 shirt, told evertontv: "I am very happy because Everton is a big club and for me it's a very good opportunity.
"I've known Everton have been following me for a while and after talking with the manager I decided coming to Everton was the best opportunity for me.
"I know this is a great club with great supporters and a club that has the ability win a lot of games in the Premier League. That's why I came."
Mirallas scored 20 goals in Greece last season, having previously played in France for St Etienne and Lille. The versatile forward has won 28 caps for his country, scoring five goals.