After the Civil War erupted, having taken a speaking tour around Ohio to encourage citizens to enlist in the Union Army, he joined the 42nd Ohio Infantry regiment with the rank of colonel. Garfield’s first task was to bring his unit, which had barely any soldiers, up to strength. He energetically, and successfully, recruited among his neighbors and old student colleagues.
In 1862, Garfield was given the command of a brigade comprising his own regiment, three other infantry units and two cavalry regiments. The brigade soon saw action at the Battle of Middle Creek, and after a hard-fought engagement, the Confederates withdrew. This battle affirmed Union control of eastern Kentucky, and Garfield, still only 30, was rewarded with the rank of brigadier general. Garfield went on to see action at the battles of Shiloh (1862) and Chickamauga (1863).