The former Barcelona star returns to LaLiga after securing a contract release from Udinese.
Sevilla have signed the ex-Arsenal and Manchester United striker to a one-year deal.
Udinese announced earlier this week: "Udinese and Alexis Sanchez are parting ways. The club and the Zebrette legend have reached an agreement for the mutual termination of their contract.
"Alexis will always be an icon in Udinese's history, and the entire club thanks him for the moments they wrote together, which will remain etched in the memories of our fans.
"Sanchez has always demonstrated the utmost professionalism and love for our colors, even when he returned to Friuli last year. The club wishes Alexis the best of luck, as he will always be our Niño Maravilla."
