John Otho Marsh Jr. served as Chairman of the Reserve Forces Policy Board from 1989 to 1994.

John Otho Marsh Jr. (born August 7, 1926) is an American politician and an Adjunct Professor at George Mason University School of Law. He served as the United States Secretary of the Army from 1981 to 1989, and as United States House of Representatives from Virginia from 1963 to 1971.

Marsh was born in Winchester, Virginia, on August 7, 1926 and graduated from Harrisonburg High School in Harrisonburg, Virginia. He enlisted in the United States Army in 1944, during World War II, and was selected at age eighteen for Infantry Officer Candidate School (OCS) graduating as a second lieutenant of infantry in November 1945, then assigned to the Army of Occupation of Germany where he served from 1946 to 1947. He was a member of the United States Army Reserve from 1947 to 1951. He graduated from Washington and Lee University in 1951, where he was a member of Phi Kappa Psi Fraternity. He entered the Army National Guard in Virginia in 1951 and graduated from the Army's Airborne School in 1964. He later retired in 1976 in the rank of lieutenant colonel.

Meanwhile, in 1952, he was admitted to the Virginia Bar, and started practicing law in Strasburg, Virginia, where he served as town judge. From 1954 to 1962, he was the town attorney in New Market, Virginia. He served in the United States House of Representatives as a Democrat from Virginia from 1963 to 1971. He fought in the Vietnam War for a month without telling his fellow soldiers he was a Congressman. In 1973, he was appointed as Assistant Secretary of Defense, and in January 1974, as National Security Advisor for then-Vice President Gerald Ford. Under President Ford, he became Counsellor to the President and held Cabinet rank. From 1981 to 1989, he served as the United States Secretary of the Army under President Ronald Reagan. Marsh was then selected to serve as Chairman of the Reserve Forces Policy Board, a position he held from 1989 until 1994. He later served as Chairman and interim CEO of Novavax, Inc., a pharmaceutical company. He still sits on its Board of Directors. He was a confidant of Dick Cheney when he was Vice President.

From 1998 to 1999, he was Visiting Professor of Ethics at the Virginia Military Institute, and Adjunct Professor of Law at The College of William & Mary from 1999 to 2000. He now teaches a course on Technology, Terrorism and National Security Law at George Mason University.

He is a former Co-Chair of the Independent Review Group for Walter Reed Hospital and Bethesda Navy Medical Center. He is a member of the Markle Foundation. The John O. Marsh Institute for Government and Public Policy at Shenandoah University is named for him.

He lives in Winchester, Virginia with his wife, together they have had three children and seven grandchildren.