"Idrissa will provide quality in our squad in the midfield and we want to increase the quality in the team," chief coach Ronald Koeman told Everton's website on Tuesday.
Gueye, 26, is Koeman's second signing since the Dutchman arrived from Southampton to replace the sacked Roberto Martinez in June, reports Xinhua.
"He was one of the players last season with the best record in interceptions and pressing in the midfield. We need this kind of quality and I'm happy to have him joining our club."
Gueye moved to Villa from French club Lille last year and made 38 appearances in all competitions as Villa were relegated from the Premier League.
"Everton is a big team with big players and great fans. The manager told me he is very happy to have me here and that we will have time to talk about football after," Gueye said.