William W. Avery was born on June 28, 1834, in Hartford, Connecticut, to Amariah and Fidelia Avery. His father was a farmer who owned $3,500 of real estate by 1850. He grew up in Windsor, Connecticut, and by 1850, he was working as a burnisher in Wallingford, Connecticut.
He enlisted in the Union army on April 20, 1861, and he mustered in as a private in Company C of the 11th New York Infantry. According to his service records, he was 5 feet, 6 inches tall, with dark hair and grey eyes. The regiment took part in the First Battle of Manassas and the Peninsula campaign. He was promoted to sergeant on February 4, 1862, and he mustered out on June 2, 1862.
He returned to the Union army on July 25, 1863, and he mustered in as a private in Company F of the 18th New York Cavalry. He eventually earned a promotion to sergeant, but he was reduced to the ranks on June 12, 1865. The regiment took part in the Red River campaign, and he mustered out on December 28, 1865.
He settled in Avon, Connecticut, after the war. He died in New York City on December 7, 1907.