The 23-year-old midfielder completed a medical and agreed terms at the club's Bodymoor Heath training ground, with the move set to be finalised next week.
Tonev played alongside Stiliyan Petrov when he made his Bulgaria debut against Wales in October 2011 and in total has played 11 times for the national team, scoring a hat-trick in the 6-0 victory over Malta in March.
He is keen to follow in Petrov's footsteps at Villa and admitted his presence at the club was instrumental in his decision to join Paul Lambert's side.
"I am really happy to be part of Aston Villa and I am really proud to be able to pull the shirt on," Tonev told the club's official website.
"Aston Villa is a big club and the manager and club have a belief in young players and in the team ethic.
"I am part of the team now and I am hungry for success. I want to show everybody what I can really do. I have played in front of big crowds before but the atmosphere here in England is unique.
"I can't wait to start and to meet my team-mates and the manager. When I heard about Aston Villa, I thought about playing in the Premier League for such a big club.
"Stiliyan being here wasn't a massive influence on me coming here. Stiliyan and Dimitar Berbatov have done really well in this league and I hope I can do the same.
"They are both great Bulgarian players and hopefully I can do the same and make my mark on the Premier League."
Petrov, who is now assistant development coach at the club after retiring from football as he continues to battle leukaemia, is convinced fans will be impressed by Tonev.
"I played alongside Aleks, so I know a little bit about what kind of a player he is. The main thing is that the manager likes him as well and the way he plays," he said.
"I think Villa fans have one exciting player on their hands. He doesn't have a dominant foot which is really interesting.
"He is the kind of player who can really make an impact in this young, exciting team. We spoke last night and he is really looking forward to it. He knows that it will be a challenge but he is ready for it."