The 30-year-old striker is set to join Saudi club al-Hilal, where he will be teammates with Karim Benzema, Ruben Neves and Kalidou Koulibaly, among others.
Watkins joined Aston Villa from Brentford in 2020 and is Villa's all-time leading scorer with more than 100 goals for the club. Last season he helped the team, which includes Victor Lindelöf, win the Europa League title and scored 16 goals in the Premier League.
"I am eternally grateful for the last six years," Watkins said in a video on social media.
Watkins was part of England's World Cup squad this summer but was short of playing time in the tournament, where the country took bronze.
