Townsend, set to undergo a medical on Tyneside tomorrow, posted a photograph of himself about to drive out of the club's Enfield training complex on Twitter.
The 24-year-old tweeted that he was "emotional".
Tottenham today accepted a £12million bid from Newcastle for Townsend, who fell out of favour at White Hart Lane late last year.
The England international needs to be playing week in, week out ahead of Euro 2016 in the summer.
Speaking to Sky Sports, Townsend said: "As soon as I knew of Newcastle's interest, they were the only club I wanted to join.
"Two of the best positions you can play in football are centre-forward and left-wing at Newcastle.
"I've got the chance – I could never turn that down.
"I can't wait to play my first game at St James's Park. I'm excited!"