The New Zealander emerged as a surprise deadline day target for the North Londoners following the news that Sebastien Bassong was to join Wolverhampton Wanderers.
Nelsen, 34, has made just one Premier League appearance this season following a knee injury, but has now signed a six-month deal with Spurs, with the option to extend it by a further year.
"We are delighted to announce the signing of defender Ryan Nelsen," a statement read on the club’s official site.
"The New Zealand international joins us from Blackburn Rovers where he spent seven years and made over 200 appearances."
The defender, who spent seven years at Ewood Park prior to his contract being terminated late on Tuesday, revealed that the opportunity to win medals at White Hart Lane proved to a driving factor to completing the deal.
"Medals, trophies are things you strive for. Blackburn got to five semis and never made a final, so it's very exciting," Nelsen told New Zealand's3News.
"[It] feels like you're going back to the first day of school, so yeah, everyone will be looking at you and judging you so I'd better clean my boots and comb my hair... it'll be fun."
By Ben McAleer
