The 43-year-old, along with his Argentinian assistant, will be tied to the Championship side until 2016.
Brighton chairman Tony Bloom said: "This is great news for the club. Gus and Tano are key to all of our immediate and long-term plans. Personally, I am absolutely delighted to have agreed these new contracts.
"They are an absolute pleasure to work with, and while they each had three seasons left on their previous contract, this gives the club even more long-term stability and further underlines their own commitment to the club."
The Seagulls, who moved into the new Falmer Stadium this season, captured the former Chelsea player in 2009.
Poyet added: "The new contracts will allow us to make even more long-term plans, particularly with regard to the new academy and training ground.
"I am delighted to extend my stay here, as the last two years here have been absolutely fantastic."
Meanwhile, Brighton take on Ipswich in an Championship clash tomorrow (Saturday).