John Otho Marsh Jr. (August 7, 1926 – February 4, 2019) was an American politician and an adjunct professor at George Mason University School of Law.

As proof of how rapidly the district was trending away from the Democrats, in his first run for the seat, Marsh only defeated Republican challenger J. Kenneth Robinson by 598 votes.

Following Marsh's retirement, Robinson, who by this time represented much of the district's western portion (including the Byrds' home) in the Senate of Virginia, won the seat easily, and the 7th would be held by Republicans until it was dismantled in 1993.

In 1973, he was appointed as United States Assistant Secretary of Defense, and in January 1974, as National Security Advisor for Vice President Gerald Ford.

"[9] Marsh was then selected to serve as chairman of the Reserve Forces Policy Board, a position he held from 1989 until 1994.

[1] At the time of his death in 2019 he was teaching a course on technology, terrorism and national security law at George Mason University.

[1][15] In 2007, when patient conditions at Walter Reed Army Medical Center had become a national concern, Marsh and former Secretary of the Army Togo West were appointed by Secretary of Defense Robert Gates to an independent review panel tasked to investigate medical and leadership failures.