The Mexico striker has signed a three-year contract at Ramon Sanchez-Pizjuan Stadium, bringing to an end his two-and-a-half season stay in east London.
The 31-year-old netted his final goal for West Ham during a 1-1 draw away at Brighton on August 17, which also marked his last appearance for the club.
West Ham have released an official statement on their website, which reads: “West Ham United can confirm that striker Chicharito has joined Spanish Primera Division club Sevilla on a permanent basis for an undisclosed fee.
“The club would like to thank Chicharito for his contribution and wish him all the best in his future career.”
Hammers chairman David Gold also confirmed the news via his Twitter account, thanking Hernandez for his service before wishing him well in Spain.
Hernandez scored 17 goals in 63 games across all competitions for West Ham in total, helping the team secure a top ten spot last season after a 13th place finish in 2017-18.
The diminutive centre-forward has not quite been able to recapture his best form at the London Stadium, but he endeared himself to the fans with his work-rate and explosiveness in the final third.