The 22-year-old midfielder makes the move north of the border once more, this time on a permanent basis after featuring on loan for Queen’s Park and Dundee FC in the past two seasons.
Boateng joined Palace at the age of 11 and progressed through the Academy, signing his first professional contract with the club in October 2019.
He will now continue his career at Hearts, who finished third in the Scottish Premiership last season.
Chairman Steve Parish said: “I would like to thank Malachi for his hard work during his time at the club, and I wish him the best for his future career.”