Tottenham boss Roberto De Zerbi revealed that Danso, 27, was one of three player that had asked to leave the club before the end of the window.
The other two, Richarlison and Pape Matar Sarr, have had mixed outcomes, with the Brazilian set to stay at Spurs, and Sarr having joined Juventus on loan.
Sunderland have now confirmed the signing of Danso on loan for the rest of the season, with an obligation to buy included in the deal.
Per David Ornstein, Sunderland will pay a loan fee of £2.5 million, and then £22.25m to make it permanent.
Danso has already agreed to a four-year contract at the club once his loan move is complete.
Speaking to the club’s website, Danso said: “I’m really happy to be here and I can’t wait to get started.
“Sunderland is a big club with huge ambition, and I’m excited to be part of what we’re building this season.
“I know Florent well from our time together at Lens, so that was an important factor in my decision. I’m looking forward to working with him again, meeting my new team-mates and experiencing the atmosphere at the Stadium of Light.”