When his father died when Comly was only ten years old, he moved to Columbus and worked in a printing shop as a messenger, before becoming an apprentice and journeyman printer.

He began writing articles for newspapers and joined the fledgling Republican Party, supporting John C. Frémont for president in 1856 and Abraham Lincoln in 1860.

When hostilities broke out between the North and South, Comly enlisted in the Union Army in December 1861, being appointed by Republican Governor William Dennison as major of the 23rd Ohio Volunteer Infantry, an appointment at first not popular with the men as several experienced captains were passed over for the political appointee, Comly.

In February 1864, when Hayes was promoted to division command, Comly was named as his successor as colonel of the regiment, which he led for much of the remainder of the war until lingering effects from battlefield wounds forced him out of the field in early 1865.

In April 1866, Comly established a local baseball team in Columbus and became the sport's major promoter and advocate in the region.