Watford have signed Nyron Nosworthy from Sunderland for an undisclosed fee, with the defender agreeing a two-and-a-half-year deal.
The 31-year-old joined the Hornets on loan in October and has played in 13 consecutive games since.
He has been at the Stadium of Light since signing from Gillingham in 2005 and featured in 114 league games for the Black Cats.
"It feels like home here," he told the Watford website.
"Credit to the manager here for the chance he gave me to play and for helping make this deal happen."
Boss Sean Dyche added: "I think this an outstanding piece of business for our club considering everything remains within the financial constraints we have here."