The 24-year-old arrives at St. James’ Park for an undisclosed fee and has signed a five-and-a-half-year deal with the Magpies. He will wear the number 25 shirt.
Townsend made 93 senior appearances in all competitions for Spurs after joining the club’s academy system aged eight.
He has also represented England at youth and senior level, earning ten full international caps and scoring on three occasions under current boss Roy Hodgson.
Andros Townsend said: “I’m delighted to be here. Newcastle United is a fantastic club with great fans, a great stadium and great tradition.
“As soon as I heard Newcastle were interested in me, there was only one place I wanted to go so I can’t wait to get started.”
Steve McClaren, Newcastle United head coach, said: “Bringing Andros to the club is a great signing.
“He is a very good talent who is a current England international and should be one for years to come, too.
“Andros is a winger with an old-fashioned style. He can play on the right or the left, is two-footed, quick, very direct and loves taking on defenders and crossing the ball.
“He feels he has a lot to prove and I can’t wait to see him do that in a Newcastle shirt.”