The French international becomes Villa's second signing high profile signing of the January transfer window following Philippe Coutinho's arrival from Barcelona.
The 28-year-old left-back, who joined Everton from Barcelona for £18m in 2018, has been tracked since falling out of favour with Rafa Benitez at Goodison Park.
Digne has won league titles in both France and Spain and represented his country at both World Cup Finals and European Championships.
And boss Steven Gerrard is delighted at securing the services of the left-back:
"When Lucas became available we jumped at the opportunity to bring him to the club," said the head coach.
“To sign a player of his pedigree and quality in the January window is a great addition to our squad and his arrival excites me and everyone associated with Aston Villa.”
Digne is expected to go straight into the squad for the home clash with Manchester United at Villa Park on Saturday.