The Argentine forward returns to his former club three-and-a-half years after departing for the Foxes for a club record fee in 2014.
Ulloa, 31, previously enjoyed an extremely profitable stint at the AMEX Stadium in his first spell. After joining the club from Spanish second-tier outfit Almeria, he scored 26 goals in 58 games over 18 months.
He was then transferred to then newly-promoted Leicester City for a fee of approximately £8million. In his time at the King Power Stadium, he scored 20 goals in 102 appearances. He netted important strikes as the Foxes survived relegation in 2015, and won the Premier League title the following season.
Despite playing in the UEFA Champions League, he has found game-time hard to come by in recent months. Ulloa has only made six appearances so far this season, with his last start coming in the 2-0 victory over Liverpool in the EFL Cup back in September.
He is currently below the likes of Jamie Vardy, Islam Slimani and Kelechi Iheanacho in the pecking order at Leicester and will aim to earn more minutes at his former club.
'There's unfinished business here'
Upon returning to Brighton, Ulloa expressed his delight at being back at the AMEX Stadium. Talking to the Seagulls' official website, he said: "It was an easy decision because I have a unique feeling with this club – they opened the door for me to come into England and I know all about the fans, the club and the city."
The Argentine also told that the club "feels like my home in this country" and that he was "happy" to be back.
Ulloa continued: "Now I have a new chapter and I want to focus on Brighton. I’ve played in the Premier League now and I’ve improved both as a player and a person.
“I feel like there’s unfinished business here and I always felt everything about the club meant it deserved to be in the Premier League."