Allen was born in Winchester, Massachusetts on August 24, 1902.^[1] In 1906 he moved to Minneapolis. He was graduated from Phillips Academy at Andover, Massachusetts, in 1922 and later attended Harvard College in Cambridge, Massachusetts.^[1] He moved to Greensburg, Pennsylvania in 1929 and was a salesman and sales manager for a valve and fittings manufacturing business until 1937.

He was district administrator of the Works Progress Administration in 1935 and 1936.

Allen was elected as a Democrat to the Seventy-fifth and Seventy-sixth Congresses. He was not a candidate for renomination in 1940. He became president of the Duff-Norton Manufacturing Company in Pittsburgh, from 1940 to 1943. He was commissioned a major in the United States Army Ordnance Corps in July 1942 and was promoted to lieutenant colonel in February 1943. He served until his discharge in January 1945.^[1]

After his time in Congress and the Army, he served in a variety of business positions:

• Baldwin Locomotive Works (Sales manager) from 1945 to 1946^[1]
• Fisher Plastics Corporation (Vice President) in Boston, Massachusetts from 1946 to 1947
• Great Lakes Carbon Corporation (Vice President) from 1947 to 1954^[1]
• Pesco Products (President), a division of Borg-Warner Corporation, from 1954–1957^[1]
• Bucyrus-Erie Company (Vice President in 1957 - 1958, and president in 1958)
• Bucyrus-Erie Co. of Canada, Ltd. (chairman of the board and president)
• Ruston-Bucyrus, Ltd., Lincoln, England (chairman of the board)
• Director of the First National Bank of Milwaukee, Wisconsin.

He retired from business activities in 1962 and moved from Milwaukee, to Keene, Virginia, where he died.

Allen married Katharine Hancock Wilson on January 17, 1925. Together, they had three children.^[1]

• United States Congress. "Robert G. Allen (id: A000145)". Biographical Directory of the United States Congress. Retrieved on 2008-01-26
• The Political Graveyard