The 24-year-old midfielder has signed a three-and-a-half-year deal with Gus Poyet's side and is reunited with the Uruguayan coach having worked alongside him during the 46-year-old's time in charge at the Amex Stadium.
Bridcutt was awarded Brighton's Player of the Season award in both 2012 and 2013 and has thus far made 11 appearances for the promotion-chasing Championship club this term.
The former Chelsea youngster becomes Sunderland's fifth signing of the January window following the arrivals of Marcos Alonso, Santiago Vergini, Oscar Ustari and Ignacio Scocco.
The Black Cats are fighting to avoid relegation from the Premier League and Wednesday's narrow 1-0 victory over Stoke City helped lift them to 17th place in the table, two points above the drop zone.
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