The clubs are believed to have agreed a fee in excess of £8m with Caulker agreeing to terms on a four-year deal.
The 21-year-old told Cardiff's website: "I want to say how happy I am to have signed with Cardiff City. I'm delighted to be here & excited for this fresh challenge.
"I spoke to the gaffer yesterday, liked what he had to say and am excited about the plans he has for the football club.
"You get the sense of excitement from everybody at the club in the build-up to the season's kick-off at West Ham and I'm really looking forward to being part of it.
"I thank Tottenham for everything they've done for me, having been there since I was a kid. But I'm here to back myself up now and show what I can do. This is a fresh start, a new chapter and I'm here to kick on."
He started 18 Premier League games for Spurs last season and spent the previous season on loan with Cardiff's rivals Swansea City, playing a further 26 top-flight games.
He made his senior England debut last November and scored in the 4-2 friendly defeat by Sweden.
Caulker is Cardiff's fourth summer signing and their new record signing, surpassing the £7.5m they paid for FC Copenhagen striker Andreas Cornelius on July 1.
Derby County defender John Brayford and Brentford goalkeeper Simon Moore have also joined the club this summer and boss Malky Mackay is keen on bringing in Toulouse midfielder Etienne Capoue as well.