Danso arrives from Tottenham Hotspur on a season-long loan worth £2.5million, with an obligation to make the move permanent for £22.5million next summer should Régis Le Bris keep the club in the Premier League.
The 27-year-old made 52 appearances for Spurs after signing from RC Lens in January 2025 and will provide the Black Cats with proven top-flight experience as they prepare for a first European campaign since 1973.
"I'm really happy to be here and I can't wait to get started," Danso said. "Sunderland is a big club with huge ambition, and I'm excited to be part of what we're building this season."
The move comes as Tottenham reshape their own defensive options following Danso's departure, having fallen down the pecking order under new head coach Roberto De Zerbi after helping the club win the Europa League last season.
At the opposite end of the experience scale, Sunderland also confirmed the signing of Juan Riquelme Angulo Caicedo, an 18-year-old striker who joins from Ecuadorian side Independiente del Valle on a long-term contract for a fee not disclosed by the club. Standing 6ft 4in, Angulo Caicedo is regarded as a physically imposing forward who nonetheless combines his size with agility and a sharp instinct in front of goal.
He made his professional debut for Independiente del Valle in March, scoring in a 3-1 win over Mushuc Runa, and was called up to Ecuador's senior squad for the first time that same month. He leaves South America with six goals in 15 league appearances this season, a return of roughly a goal every 115 minutes, for a side sitting 21 points clear at the top of Ecuador's top flight, having previously drawn interest from clubs across Europe during his rapid rise.
Director of football Florent Ghisolfi said the club had fought off considerable competition to land the teenager.
"There were a lot of big clubs around Europe chasing his signature, so this signing demonstrates the attraction of Sunderland AFC," Ghisolfi said.
"His physical qualities are obvious, but he also has good movement, technical ability and a natural instinct for scoring goals. He has already shown in a short spell that he can compete at senior level despite his age, and we are delighted to bring him to Sunderland at this important stage of his development."
Between the loan capture of a Premier League-tested centre-back and a teenage forward considered one of Ecuadorian football's brightest emerging talents, Sunderland's deadline-day business reflects a squad being strengthened for the immediate challenge of survival and the club's longer-term ambitions alike.