At Aston Villa, Jackson is reunited with coach Unai Emery, who coached Villarreal during the player's time at the Spanish club.
Last season, Jackson was on loan to Bayern Munich, where he helped the club to both the league and cup titles in Germany with his eleven goals.
The 25-year-old has made 37 appearances for Senegal's national team, and was part of the country's World Cup squad that reached the round of 16 in this summer's championship.
