He graduated from the United States Military Academy in 1925 and was commissioned as a Second Lieutenant of Cavalry. He graduated from the Cavalry Officers Course in 1930. In 1942 Harrold graduated from the Command and the General Staff College.
He was commander of the 9th Armored Division, United States. Army Armor School, 1st Cavalry Division, 8th Infantry Division, 10th Mountain Division, III Corps, and United States. Army Caribbean. From 1958 to 1961 he served as commandant of the National War College. From 1926 to 1927 Harrold was the adjutant for the 7th Cavalry Regiment.
Harrold served as an instructor at West Point in the early 1930s.
In the early 1940s Harrold was in charge of Army recruiting for the area that included Connecticut. During Harrold commanded Combat Command A, 9th Armored Division, serving from August 27, 1944 to May 3, 1945.
Harrold led his command during combat in Europe, including a key role in repelling the Germans during the Battle of the Bulge. Harrold commanded the 9th Armored Division from 1945 to 1946.
From 1946 to 1947 Harrold served as commander of the 3rd Constabulary Brigade in West Germany.
Harrold served as Director of Civil Affairs for the United States. Army European Command from 1947 to 1949. From 1949 to 1951 Harrold served as commander of the United States. Army Armor School and Fort Knox. Harrold briefly served as deputy commander of I Corps in 1951, but was soon transferred to commander of the 1st Cavalry Division.
He served from July, 1951 to March, 1952, receiving promotion to Major General and leading the division the Harrold commanded the division during its stationing at Hokkaido, the northernmost island in Japan, where it carried out combat training, electronic surveillance and defense of Japan from potential attacks by the Soviet Union or China.
From February, 1953 to June, 1954 Harrold was commander of the 10th Mountain Division. Harrold commanded the 8th Infantry Division from August to November, 1954.
General Harrold served as commander of the III Corps at Fort Hood from 1954 to 1956 From 1956 to 1958 Harrold served as commander of the United States. Army Caribbean. Harrold was Commandant of the National War College from 1958 until his 1961 retirement.
In retirement General Harrold resided at Fort Lauderdale, Florida, where he died on June 16, 1973.
He was buried at Arlington National Cemetery, Section 2 Site East-508. General Harrold was married to Emily Draper of Troy, New New York They had one child, Sally, who was born in 1937.