When the civil war began he raised a company of Irish Americans and served with them in the 10th Ohio Infantry under William Haines Lytle for three months, afterwards re-enlisting in the 10th for three years. At the Battle of Carnifex Ferry he received a gunshot wound through the right lung. As soon as he recovered he returned to the field and was appointed colonel of the 50th Ohio Infantry by the Governor of Ohio David Tod. The 50th was afterward merged into the 61st, and he commanded the latter till the end of the war. At the Battle of Peachtree Creek on July 20, 1864 his left arm was shattered at the elbow by a minié ball in the beginning of the engagement, yet he remained with his men through the fight. He was accustomed to expose his life with the utmost hardihood, and during the war received twenty-three wounds. He was brevetted brigadier-general of volunteers on May 1, 1865. He was for two years collector of internal revenue, and just before his death, which resulted from injuries received in battle, was elected clerk of the Hamilton County, Ohio courts.