The Denmark midfielder capped a frantic day at White Hart Lane when he became the club's third signing in 24 hours, joining Vlad Chiriches and Erik Lamela.
Eriksen has moved for an undisclosed fee and, even though his arrival gives another nod towards Gareth Bale's impending departure to Real Madrid, a switch to Tottenham's new-look squad was much to his delight.
"Everyone has followed the development of Spurs and it's something I want to be part of," he said.
The 21-year-old has already represented his national team on 37 occasions, scoring four goals, and was a key player for Ajax, having moved there from Odense in 2008.
He made 161 appearances and helped the Amsterdam side win three successive Eredivisie titles from 2011, and signs for a Tottenham side that bolstered their ranks immeasurably on Friday.
Chiriches became the club's fifth summer purchase on Friday morning when he completed his #8.5million move from Steaua Bucharest and four hours later, Tottenham confirmed that they had signed 21-year-old Lamela for fee thought to be around #25.8million.