Marcus A. Emmons was born around 1840 in Massachusetts to Alonzo and Abigail Emmons. His father was a farmer who owned $700 of real estate in 1850. Emmons grew up and attended school in Hardwick, Massachusetts. By 1860, he was working as a farm laborer. He enlisted in the Union army on July 19, 1861, and mustered in as a private in Company K of the 21st Massachusetts Infantry later that day. The regiment took part in the Battles of New Bern, Second Bull Run, Antietam, and Fredericksburg. He was promoted to corporal on November 10, 1862. He died at Bethesda Church in Virginia on June 2, 1864.