John W. Comfort was born in Philadelphia, Pennsylvania, in 1844. At the start of the American Civil War, the 17-year-old Comfort joined up with the 29th Pennsylvania Volunteer Infantry on June 20, 1861. He immediately reenlisted while stationed in Hamilton County, Tennessee in December 1863, weeks after the Battle of Wauhatchie, and was promoted to the rank of sergeant at the end of the month. Comfort saw continuous action around Chattanooga, Tennessee and in Georgia, including the sieges of Atlanta and Savannah, as well as the Carolinas. After the war's end, Comfort was honorably discharged on July 17, 1865. He decided on a career in the military, however, and enlisted in the Regular United States Army four months after leaving the volunteer service.