Harley Martin Kilgore (January 11, 1893 - February 28, 1956) was born in Brown, West Virginia, to Quimby and Laura Martin Kilgore. He received his LL.B. from West Virginia University in 1914 and was admitted to the bar the same year.

He taught school in Hancock, West Virginia in 1914 and 1915. Also in 1915, he organized the first high school in Raleigh County, WV, and served as principal. He established his law practice in Beckley, WV in 1916. During World War I, he served in the infantry from 1917 and was discharged as a captain in 1920. Kilgore married Lois Elaine Lilly in Huntington, WV on May 10, 1921. That same year, he helped organize the West Virginia National Guard, and was promoted to major and appointed commander of 2nd Battalion the following year. He also served as Beckley city recorder in 1922. His son, Robert Martin Kilgore, was born in 1924. His daughter, Elinor Stuart Kilgore, was born in 1926.

In 1932, Kilgore was assigned to the state headquarters of the National Guard. He was elected judge of the Raleigh County criminal court from 1933 to 1940 on the Democratic ticket. In 1940, he was elected to the U.S. Senate with support from the Neely faction of the Democratic Party, and won reelection in 1946 and 1952. Also in 1940, he was placed on active military duty as judge advocate for West Virginia's Selective Service system until he entered the Senate. A member of the U.S. Senate from 1941 until his death, Kilgore served as chairman of the Judiciary Committee and the Committee to Investigate the National Defense Program. In October 1942, he became chair of the Subcommittee on War Mobilization of the Military Affairs Committee (also known as the Kilgore Committee).

In 1948, Kilgore served as a delegate at the Democratic National Convention, where he was an outspoken supporter of Harry S. Truman. He retired from the West Virginia National Guard as a lieutenant colonel in 1953. He died in 1956 at age 63 at Bethesda Naval Hospital, and was buried at Arlington National Cemetery.