Defense Secretary Chuck Hagel said that he met with Carter Thursday morning and "reluctantly accepted" his decision to step down.
Carter, now 59, "possesses an unparalleled knowledge of every facet of America`s defense enterprise, having worked directly and indirectly for eleven secretaries of defense over the course of his storied career," Hagel said in a statement.
The exact reason for Carter`s departure was not immediately known. It was also unclear who might replace him.
Carter has served as the Pentagon`s second-ranking official for two years under Hagel and his predecessor Leon Panetta. Before that, he was undersecretary of defense for acquisition technology and logistics under Defense Secretary Robert M. Gates. As undersecretary, Carter worked to increase the department`s buying power and to strengthen America`s defenses against cybersecurity. (*)