The 26-year old Argentine striker has signed a four-and-a-half-year contract with the Seagulls after spending the past four-and-a-half years in Spain's Segunda Division with both Castellon and Almeria.
"Leo is that striker we have been looking to add for some time. He will complement our existing strikers, enjoy playing with our wingers and creative players," Brighton boss Gus Poyet told the club's official website.
"He's a typical number nine box player; he's good in the air, he will hold the ball up and he has good movement around the box when the ball is wide.
"He will suit the way we play, fit in well to our style and identity and I am sure he will make us a stronger team.
"I know him from Argentina and I follow Spanish football closely so I have been aware of him for a while, but the problem was that he was not available because he didn't have a European passport.
"However, that situation has changed since the last transfer window, and as soon as we knew there was a chance of getting the passport sorted, the recruitment system moved very quickly."