Pau Torres' transfer fee is reported to be about £31.5m
Torres, 26, played under Villa boss Unai Emery with the Spanish club between 2020 and 2023.
The defender, who joined Villarreal's youth academy in 2003, played a pivotal role as the Yellow Submarine finished fifth in La Liga last season.
He made 173 appearances for his boyhood team, scoring 12 times, and has played 23 times for Spain.
Torres made his first Villarreal appearance in 2016, becoming the first player born in the small Valencian town to debut for the club in 13 years.
He quickly established himself as a key player in the squad, winning the 2021 Europa League under Emery when he was among the scorers in the penalty shootout victory over Manchester United.
Torres made his debut for Spain in 2019 and has played both at Euro 2020 and the 2022 World Cup.
He is Aston Villa's second summer signing, after Belgium midfielder Youri Tielemans arrived on a free transfer from relegated Leicester City.
Villa finished seventh in the Premier League last season, securing qualification for the Europa Conference League.
-- Courtesy of BBC Sport