In 1861, Tyler was elected colonel of the 7th Ohio Infantry. On May 14, 1862, Tyler was commissioned as a Brigadier General. He was assigned to a number of units in his career. In June 1862, he commanded Union forces at the Battle of Port Republic with his forces outnumbered almost two to one. In December 1862, he was wounded at the Battle of Fredericksburg. After the Battle of Chancellorsville, his men mustered out of service, so Tyler was transferred to the defenses of Baltimore, Maryland. He remained at or near Baltimore until the end of the war. He was involved in the battle of Monocacy in defense of Washington. He resigned from service in April 1865.