Nelson W. Bennett was born on February 1, 1838, in Russell, Massachusetts, to Benjamin and Almira Bennett. His father was a farmer who owned $1,220 of real estate and $485 of personal property by 1860. He grew up and attended school in Russell, and by the early 1860s, he was working as a butcher.
He enlisted in the Union army on October 25, 1861, and he mustered in as a private in Company B of the 31st Massachusetts Infantry. According to his service records, he was 5 feet, 8 ½ inches tall, with brown hair and grey eyes. He eventually earned a promotion to sergeant. He died near Alexandria, Louisiana, on May 14, 1864.