He scored 26 goals in 58 appearances for Brighton and helped them to reach last season's Championship play-offs.
Boss Pearson said: "We identified Leo as a player that could help us move forward quite some time ago.
"He has adapted extremely well to the English game in a relatively short period of time and I'm sure he will have a great deal to offer us in the Premier League.
"He complements the forwards we already have very well and his attributes broaden the options available to us, which will be important this season.
"I'm delighted we've been able to add him to the squad."
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