Barkley was in danger of falling out of the picture with Chelsea and England following the Blues’ close-season signings of Kai Havertz and Hakim Ziyech.
The 26-year-old had made only three appearances for Frank Lampard’s side this season.
Overall, Barkley has started just 28 Premier League games in a Chelsea shirt since arriving from Everton in 2018.
With the European Championships next year, he wants to force his way into Gareth Southgate’s plans and believes more regular playing time at Villa will give him a better chance.
“The last couple of years I’ve been stop-start, performing well and then being out of the team,” Barkley told Villa’s website.
“To come here and have the chance to play and perform regularly is a big thing for me. With the Euros at the end of the season, it’s a big target for me and hopefully I can be there.
“Dean Smith swayed me with the way he spoke to me, and it looks like it’s going to be an exciting season.”
Jack Grealish has starred in Villa’s unbeaten start to the season and Barkley revealed the club’s captain played a part in convincing him to join.
“We’re mates off the field and we know each other well,” Barkley said.
“We’ve spoken previously and I’m looking forward to playing with him.
“I’ve spoken to him over the past couple of weeks and he’s been telling me about how good the club is and how welcomed I’d be when I came here.”
Villa manager Dean Smith added: “Capturing a player of Ross’s quality is a real coup for our club and I am certain he will thrive here and improve our team.”
Barkley will be unavailable for Thursday’s League Cup visit of Stoke, having already played in the competition for Chelsea this season.
Smith’s side have won their opening two Premier League games and Barkley could make his debut against Liverpool on Sunday.
