Defense Minister Jean-Yves Le Drian, leading France's military operations against Islamic extremists in Syria and Iraq, announced the move in Ouest-France newspaper today.
Le Drian's support adds weight to Macron's centrist campaign, and comes after two other members of President Francois Hollande's Socialist government joined Macron.
However Macron is being careful not to associate himself too closely with Hollande's unpopular outgoing administration and the divided Socialists.
Macron, a former banker with pro-market views who has never held elected office, is considered the front-runner for the two-round vote April 23 and May 7.