Villa have announced on their official website that they have signed Watkins from the Bees on a five-year contract.
According to BBC Sport, the Villans have paid the London club an initial transfer fee of 28 million pounds to secure the services of the forward, who can play as a forward or as an attacking midfielder.
The 24-year-old was one of the best players in the Championship last season and played an important role in the Bees reaching the playoff final.
The Englishman scored 26 goals and provided three assists in 49 Championship matches for Brentford last season.
Watkins is over the moon to have joined Villa and is looking forward to getting started for the Villans in the Premier League.
The attacker told Villa’s official website: “I’m delighted. It’s been a long time coming but I’m buzzing it’s done now, I can’t wait to get going.”
The 24-year-old added: “It’s a massive club. Dean sold it to me, really. I’m definitely excited to get back working with Dean, I’m really looking forward to it. He sold it to me as soon as I met him.
“I told my agent I really want to get that sorted as soon as I heard they were interested. I’m looking forward to working with him and Rich (O’Kelly), they gave me a lot of confidence playing under them at Brentford. Hopefully they can do that again now.”