Wolcott Pascal Marsh was born March 15, 1839, in Brooklyn, New York. By 1860, he had moved to Hartford, Connecticut, and married Anna Thompson. For a short time, he worked selling knives. In April 1861, he enlisted in Rifle Company A, 1st Connecticut Infantry, was discharged after the First Battle of Bull Run, and was mustered into Company A, 8th Connecticut Infantry, as a second lieutenant. On December 24, 1861, Marsh was promoted to first lieutenant. Under Brigadier General Burnside in the North Carolina Expeditionary Corps, his unit fought at Roanoke Island, New Bern, and Fort Macon in the spring of 1862. Marsh was promoted to captain in December. After the Battle of Fredericksburg, Marsh received a medical discharge, probably for complications caused by malaria. By 1870, he had settled in Springfield, Massachusetts, with his wife and children and was working as a merchant.