Oscar L. Williams was born around 1842 in New London, New Hampshire, to John and Lydia Williams. His father was a farmer who owned $1,000 of real estate and $507 of personal property by 1860. Williams grew up and attended school in New London, and by 1860, he was working as a shoemaker.
He enlisted in the Union army on August 15, 1862, and he mustered in as a private in Company F of the 11th New Hampshire Infantry on August 29. The regiment took part in the Battle of Fredericksburg and the siege of Vicksburg. He died of lung congestion in Annapolis, Maryland, on April 18, 1864.