Born in Lima, Tyler County, W.Virginia, Allen attended the country schools, Fairmont Normal School, and Peabody College, Nashville, Tennessee. He was graduated from the literary department of the West Virginia University in Morgantown in 1894 and from its law department in 1895. He was admitted to the bar in 1895 and commenced practice at Morgantown, Monongalia County, W.Virginia. He served as member of the city council from 1895 to 1917. Deputy collector of internal revenue for the district of West Virginia 1917-1921. He served as judge of the city court 1921-1923.
Allen was elected as a Democrat to the Sixty-eighth Congress (March 4, 1923-March 3, 1925). He was an unsuccessful candidate for reelection in 1924 to the Sixty-ninth Congress and for election in 1926 to the Seventieth Congress. He resumed the practice of law in Morgantown, W.Virginia, until his retirement in 1927. He moved to Preston County, W.Virginia, and operated a summer resort at Brookside 1929-1939. Resided in Aurora, W.Virginia, until his death in Mountain Lake Park, Maryland, January 28, 1951. He was interred in Kingwood Cemetery, Kingwood, W.Virginia.