U.S. Army Secretary John McHugh will be leaving his post in November. (AP Photo/Ted S. Warren, file)

John McHugh, secretary of the U.S. Army, will step down by November, the Defense Department said Monday, adding to a growing list of senior military personnel who are departing the Pentagon during President Obama’s final period in office.

McHugh, a former Republican congressman, has been the Army’s top civilian since 2009. He expressed a wish to leave his post several weeks ago, the Pentagon said in a statement, and has told the president that he would step down by Nov. 1. The Pentagon did not say why McHugh was leaving, and McHugh’s office declined to elaborate.

The news of McHugh’s departure comes as Army Chief of Staff Raymond T. Odierno, a former commander of U.S. forces in Iraq, also prepares to step down. Obama has selected Gen. Mark A. Mille, who heads U.S. Army Forces Command, to replace Odierno.

[Gen. Mark A. Milley selected to be next Army chief of staff]

While McHugh’s departure after six years in the job may not be a surprise, it intensifies the pace of turnover at the most senior levels of the military. In February, Defense Secretary Ashton B. Carter became Obama’s fourth secretary of defense, while Army Gen. Martin Dempsey will step down as chairman of the Joint Chiefs of Staff this fall.

McHugh began his career in New York politics, and later served nine terms in the U.S. House of Representatives, where he exercised influence over the Pentagon as ranking member of the House Armed Services Committee.

As Army secretary, he managed the largest military service as soldiers streamed home from the war in Iraq and as they flowed into Afghanistan to fight in the surge there. He has been forced to grapple with deep cuts to defense spending and plans to shrink the size of the Army. The active component of the service is expected to shrink from about 540,000 soldiers in 2014 to 490,000 by the end of 2017.

McHugh “has helped lead the Army through a period of challenge and change,” Carter said.