Carroll was one of a clutch of players to sign new contracts at White Hart Lane during the first half of the 2016-17 season. The 24-year-old signed an extension in September that would have kept him at the club until 2019, but has now returned to south Wales having signed a three-and-a-half year deal with Paul Clement's side.
Carroll spent the 2014-15 season on loan at the Liberty Stadium and is excited to return to a club he believes suits his playing style.
"It's been a couple of years since I've been here – there have been some changes – but I'm excited to be back," Carroll told the club's official website. "It definitely helps knowing quite a few of the lads from my loan spell, while I know [assistant coach] Nigel Gibbs and [head of physical performance] Karl Halabi too.
"Knowing the players and staff allows you to settle quicker than normal. It can take time to settle in at a new club, but having some familiar faces around the place will help me get going straight away.
"I know what the club is about too, and I know the playing style suits me so that was a big factor in me coming here."
The former England Under-21 international becomes Swansea's third signing of the January window as Clement attempts to build a squad capable of keeping the club in the top flight of English football.
PSV Eindhoven winger Luciano Narsingh and Norwich City left-back Martin Olsson have already joined the club during the winter window.
Carroll leaves White Hart Lane having made 56 appearances for the club since making his senior debut in 2011, scoring three goals.