The Argentine striker has moved to the King Power Stadium on a four-year deal after firing 16 goals for Albion last term.
Ulloa previously plied his trade with Castellon and Almeria in Spanish football and will complement an attacking line-up that includes the likes of David Nugent, Jamie Vardy and Chris Wood.
Having helped Brighton to the Championship play-off semi-final last term, before losing to Derby County, Ulloa will have the chance to feature in the English top flight for the first time.
Leicester boss Nigel Pearson said the 27-year-old would serve as an ideal foil for his fellow forwards this season.
"We identified Leo as a player that could help us move forward quite some time ago," he told the club's official website.
"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.
"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."
Ulloa could make his Leicester debut in Sunday's pre-season friendly against Everton in Bangkok.
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