Ajax said in a statement that the transfer fee included bonuses with a maximum of 12.0 million euros for the 25-year-old who skippered Ajax to their second successive Dutch League title last season.
"We are delighted to announce that we have reached agreement with Ajax for the transfer of Jan Vertonghen, subject to a medical," Tottenham said.
Vertonghen becomes the second major signing at Spurs since Andre Villas Boas was named manager last week, following the signing of Icelandic midfielder Gylfi Sigurdsson from Hoffenheim on Wednesday.
Vertonghen was named as the Dutch League's Player of the Year as well as Ajax's Player of the Year last season. He made 220 appearances for Ajax and scored 28 goals for them after making his debut in 2006.
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