Villa have completed the transfer for a fee of around £2.5million with Tonev finishing a successful medical already at Villa Park.
The 23 year old has been prolific for Bulgaria in the World Cup qualifiers this year with 3 goals and 1 assist in 5 appearances to date.
"Aston Villa is a big cluband the manager and club have a big belief in young players and in the team ethic." Tonev said on the official club website.
Tonev also added, "Stiliyan and Dimitar Berbatov have done really well in this league and I hope I can do the same," Tonev said. "They are both great Bulgarian players and hopefully I can do the same and make my mark on the Premier League."