William was born on the 10th of September 1840, in Providence, Rhode Island and he was twenty-one years old when he enlisted in Company A of the 1st Rhode Island Volunteer Infantry on the 2nd of May, 1861. He served in the First Battle of Bull Run and then was commissioned as a 1st Lieutenant but with Company B of the 1st New York Marine Artillery. It was William's actions during the Battle of Tranter's Creek on the 5th of June, 1862, that would earn him the Medal of Honor. The citation reads:

Handled his battery with greatest coolness amidst the hottest fire.

William was also promoted to Captain because of his actions and would eventually muster out of service on the 31st of March, 1863. He was married to Ann Osborn and they had three children, Eliza, William, and Sybil. William Bailey Avery died on the 19th of July, 1894 at the age of 53 and is buried with his wife and two of their children in the North Burial Ground in Providence, Rhode Island: Section 13, Lot 2336.