Benjamin Mayberry Prentiss was born on November 23, 1819 in Belleville, Virginia. His family moved west to Hannibal, Missouri and later Quincy, Illinois. During the Mexican War, Prentiss served as a captain in the 1st Illinois Infantry and fought at the Battle of Buena Vista. After the war, he returned to Illinois and practiced law. He continued to serve in the militia, eventually reaching the rank of colonel. Prentiss unsuccessfully ran for U. S. Congress in 1860 as a Republican.
When the war broke out, Prentiss led Union troops in Missouri operating against the Confederate Missouri State Guard. He commanded a division in Ulysses S. Grant’s army at Shiloh, where his men bore the brunt of the Confederate assault around the Hornet’s Nest on April 6th, 1862. Prentiss was captured in the fighting there, and he was paroled in October. He served on the court-martial board that convicted General Fitz John Porter, where he voted for Porter’s acquittal. In March, 1863, Prentiss was sent to Arkansas where he led Union forces to victory at the Battle of Helena on the Mississippi River on July 4th that year. Later that year he resigned his commission to tend to family matters.
After the war, Prentiss became a lawyer and served as postmaster of Bethany, Missouri. He was also active in Missouri Republican politics, serving as a delegate to the 1880 and 1884 national conventions but he never again ran for public office. He died on February 8, 1901 and is buried in Harrison County, Missouri