The 22-year-old has signed a two-year deal at Tynecastle and becomes the club’s second recruit in two days following the arrival of former Dundee United midfielder Morgaro Gomis.
Hearts' transfer embargo ended earlier this week after the club came out of administration, and manager Robbie Neilson is delighted to secure the services of the former Celtic youngster.
Keatings scored 15 goals last season to help Accies to promotion to the Scottish Premiership, where Hearts are looking to return to at the first attempt.
Neilson said: "I've known him for a number of years and watched him at Celtic where he scored a lot of goals in the youth teams and U20s.
"The pleasing thing with James is that he had the opportunity to stay at Celtic a year ago, but because he didn't see a pathway for himself he decided to take the opportunity to leave and go to Hamilton.
"He dropped down to try to forge a career and to see that desire is great. He had the ambition to go out and take a chance and try to prove himself in a first-team environment. He did fantastically well for Hamilton at the start of last season but then picked up an injury.
"He could have stayed and played in the Premiership with Hamilton but he recognises that there's an opportunity here for him to progress. I'm pleased to get him. He's a good character and a top development prospect for us."