William Line was born around 1843 in Pennsylvania to James and Elizabeth Line. His father was a clerk who owned $2,000 of real estate and $500 of personal property by 1860. He grew up and attended school in Maunch Chunk, Pennsylvania, and by 1860, he was working as a farmer.
He enlisted in the Union army on September 16, 1861, and he mustered in as a private in Company G of the 81st Pennsylvania Infantry. According to his service records, he was 5 feet, 6 ¾ inches tall, with auburn hair and blue eyes. He died in the Battle of Fair Oaks on May 31, 1862.