The 23-year-old has agreed terms and passed a medical and the final paperwork on the move will be completed next week.
"I am really happy to be part of Aston Villa and I am really proud to be able to pull the shirt on," Tonev said.
"Aston Villa is a big club and the manager and club have a belief in young players and in the team ethic.
"Football is not about the individuals. It's a team sport and all successful teams play well together.
"That's what you can see at Villa, the team is playing together. 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. I wasn't thinking about anything else."