Frederick Carlton Weyand was born in Arbuckle, California, on 15 September 1916. He attended the University of California at Berkeley, and was commissioned a second lieutenant in the Army through the Reserve Officers Training Corps program, in 1938. He married Arline Langhart in 1940.
From 1940 to 1942, he served with the 6th Artillery, and received a promotion to temporary first lieutenant, and then to captain and major. Weyand then graduated from Command and General Staff College in 1942, before becoming an adjutant of the Harbor Defense Command in San Francisco. Weyand was assigned to the Office of the Chief of Intelligence, War Department General Staff in 1944; then he served as assistant chief of staff for intelligence in the China-Burma-India theater until the close of World War II.
Weyand returned to Washington, D.C., to serve in the Military Intelligence Service until 1946. He was made a temporary lieutenant colonel in 1945 and a permanent captain in 1948. From 1946 to 1949, he was chief of staff for intelligence, United States Army Forces, Middle Pacific. Weyand graduated from the Infantry School in 1950.
During the Korean War, Weyand was a battalion commander in the 7th Infantry and then assistant chief of staff, G-3, of the 3d Infantry Division. He returned to teach at the Infantry School from 1952 to 1953. Afterwards, he attended the Armed Forces Staff College. From 1954 to 1957, Weyand served as a military assistant to the Secretary of the Army; at this time he received a promotion to permanent major and temporary colonel. In 1958, he graduated from the Army War College, and commanded the 3d Battle Group, 6th Infantry, Europe, until 1959.
In 1960, Weyand became a temporary brigadier general. He then served as the chief of staff, Communications Zone, U.S. Army, Europe, until 1961. From 1961 to 1964, Weyand was a chief of legislative affairs in the Department of the Army; he received promotions to permanent lieutenant colonel and temporary major general.
He led the 25th Infantry Division in Hawaii and in Vietnam until 1967, and then became the commander of II Field Force in Vietnam. Weyand was promoted to permanent colonel, too. In 1968, he was made a permanent brigadier and major general, and a temporary lieutenant general. In 1970, he was again promoted, to temporary general. Weyand acted as a military advisor to the Paris Peace talks in 1969 and 1970. He served successively as assistant chief of staff of force development, deputy commander, and then commander of the United States Military Assistance Command, Vietnam, from 1970 to 1973. Then he served as commander in chief, United States Army, Pacific, before becoming vice chief of staff of the Army. When Chief of Staff Creighton W. Abrams, Jr., died in office, Weyand was promoted to Chief of Staff. He served in the post from 3 October 1974 to 31 September 1976. He retired from active service in 1976.