Caulker will join up with Swansea City for their first season in the Premier League and will finalise the move next week.
The deal will see the Swans pay an initial fee for the defender with the option to review the loan if it is needed in January.
Caulker is highly rated at White Hart Lane and spent last season on loan at Bristol City where he won a host of awards including young player of the year.
Swans Chairman Huw Jenkins told the official site "We are delighted to have agreed terms with Tottenham regarding a deal for Steven.
"The deal has been very close for the last couple of weeks. I met (Tottenham chairman) Daniel Levy at a Premier League meeting in Darlington and spoke at length about Steven.
"We feel his general size and ability are perfect qualities to add to our team.
"Steven is a young, upcoming player that is a big talent, and he is looking forward to being part out our squad in the Premier League.
"It is an exciting signing for us. There was other interest in him prior to this deal being agreed, but Tottenham felt it was perfect for Steven to continue his deal here."