George Lyman Barnes was born around 1837 in Waltham, Massachusetts, to Thomas and Adaline Barnes. His father was a farmer who owned $7,000 of real estate and $2,000 of personal property by 1860. He grew up and attended school in Waltham, and by 1860, he was working as a clerk. He married Sarah C. Buttrick on August 28, 1860, and they apparently had no children.
He enlisted in the Union army, and he mustered in as a sergeant in Company B of the 32nd Massachusetts Infantry on October 30, 1861. According to his service records, he was 5 feet, 11 ½ inches tall, with brown hair and blue eyes. The regiment took part in the Second Battle of Manassas and the Battle of Antietam. He was promoted to 2nd lieutenant in July 1862, and he was discharged for disability on November 22, 1862.
He returned to Waltham after leaving the army, and he earned a living as a bookkeeper. He applied for a federal pension in November 1870, but he apparently never received one. He died of consumption in Waltham on June 11, 1873.