Born in a log cabin in Greene County, Ohio, he early showed an eagerness for reading, often studying beside the fire at night after a long day spent working in the fields. As a young man, he became a backwoods Methodist minister, and then worked for a Quaker-run abolitionist paper. At the outbreak of the American Civil War, he joined, with the rank of First Sergeant, the 8th Indiana Infantry Regiment, a regiment of volunteers formed for a three-month period of service; the regiment fought at the Battle of Rich Mountain under the command of William Rosecrans. He spent the remaining war years as editor of the "Winchester Journal" in Randolph County, Indiana, where he began corresponding with Charles Eliot Norton, the secretary of the Loyal Publication Society, beginning a lifelong friendship. In Norton’s papers we see Harrison described as a figure much like Abraham Lincoln: an unaffected frontiersman, at once virtuous and wise.