The 22-year-old has put pen to paper on a deal which will keep him at Villa Park until the end of the 2015-16 campaign.
Westwood helped Crewe gain promotion to League One last season and is now relishing a crack at proving himself in the Premier League.
"I see myself as a Michael Carrick-type of player, someone who stays out of the limelight and keeps it simple, retaining the ball and laying it off to team-mates," he said.
"From the conversations I've had with the new manager (Paul Lambert) I think that will fit in perfectly here.
"He said to me that he's looking for younger lads to work with him, step up and lift this club to the next level and I'm really looking forward to the challenge.
"This is a fantastic football club, a massive club and I can't wait to get started really. It's a bit surreal right now but I'll get out training with the lads tomorrow morning and take it in my stride."
Westwood - a product of the Crewe Academy - is Villa's seventh signing of the summer, and Paul Lambert is pleased with his bit of business.
"Being captain of his football club at 21 years of age, I think that says a big thing about Ashley's quality, the responsibility he has taken on his shoulders and his temperament," Lambert added.
"He's also a terrific prospect for this football club - a real, real talent.
"He's had a really good grounding at Crewe and he will fit in with what we're looking to do here. He's a good player and he'll do fine."
