The 23-year-old midfielder, placed on the transfer list by Leeds manager Neil Warnock at the end of last season, has signed a three-year deal with the newly-promoted Terriers and teams back up with Town boss Simon Grayson.
"Adam is a good footballer," Grayson told Huddersfield's official website. "He handles the ball and has a good energy about him - he had a great season last year and scored some important goals. We're delighted to have got him.
"He's a player I admired when he was at Carlisle and Manchester City and we're delighted to secure his services to this football club. I think it shows our intent in the level of players we want to sign."
Manchester City academy graduate Clayton, who has had loan spells at Carlisle, Peterborough and MK Dons, scored six goals in 43 League appearances last season for Leeds. He signed a permanent deal at Elland Road in August 2010 following a loan spell.
Clayton is Grayson's fourth summer signing following the earlier arrivals of Sean Scannell, Paul Dixon and Oliver Norwood.