Born in 1913, Iowa City, Iowa, native Sewell Ellyson Allen graduated from high school in Onawa, Iowa. He returned to Iowa City to attend law school, receiving his degree in 1939. Two years later, Allen was elected as a Democrat to Iowa's state legislature. He was defeated in the following election for a senate seat. In 1946, he was a candidate for the U.S. House of Representatives. In 1952, he ran for lieutenant governor, only to be defeated once again.
He remained active in the state's Democratic Party and for a long time was the Monona County Democratic Chairman. From 1963 through 1965 he served as the Monona county attorney and from 1965 through 1967 he worked in the Iowa attorney general's office. Sewell E. Allen died in 1975, at the age of sixty-two.