The move, which will be on a loan basis until Driver's contract expires at the end of the season, has now been officially announced on the club's website.
A statement read: "Hearts can reveal that Andrew Driver has left the club to pursue his career in the United States.
"Andrew has made 28 appearances in a Hearts shirt this season, scoring twice. He leaves Gorgie with a Scottish Cup winner's medal, following his impressive display in the 2012 final, when Hearts brushed aside city rivals Hibs 5-1.
"The club wishes Andrew all the best as he continues his career with this fantastic opportunity to play in America."
Driver made 158 appearances and scored 19 goals during his seven-year spell with the Edinburgh team.