On 17 July 2015 Sevilla FC reached an agreement with Bordeaux for the transfer of Mariano, with the player signing a three-year deal. He made his debut on 11 August in the UEFA Super Cup, coming on in the 80th minute for Kévin Gameiro in a 5–4 extra-time loss to fellow Spaniards FC Barcelona in Tbilisi. Mariano made ten more European appearances as the Andalusians went on to win the UEFA Europa League – scoring his sole goal to cap off a 5–2 aggregate win over FC Shakhtar Donetsk in the semi-finals – including the entirety of the 3–1 victory over Liverpool in the final.