Although normal for most of his childhood, Sprague began losing weight at age 12. In 1865, he joined a circussideshow, becoming "the Living Skeleton" or "the Original Thin Man". The next year P. T. Barnum hired Sprague to work at his (newly reopened) American Museum until it burned down in 1868, continuing off and on to tour him throughout the country. By the age of 44, he was 5 feet and 6 inches tall with a weight of only 43 pounds. He died, in poverty, of asphyxia.
He married Minnie Thompson and the couple had three strong, healthy, robust sons.