Pennell grew up in Kansas City, but moved to St. Louis, where he initially worked in radio, writing advertising copy for KMOX, taught at John Burroughs High School, and acted in summer stock theatre. His most famous novel, set during the Civil War, The History of Rome Hanks, was nominated for a Pulitzer Prize. Its film rights were sold for $50,000, although it was banned in Boston because of its "raw vulgarity." He married Elizabeth Horton in 1945 and, when she died, he married her sister. He wrote several other novels, but none received the reputation of Rome Hanks. He died in Porland, OR.