George W. Thompson was born around 1840 in Maine to Zenas and Leonora Thompson. His father was a clergyman who owned $2,000 of real estate and $200 of personal property by 1860. He grew up and attended school in Augusta, Maine, and the family moved to Bethel, Maine, in the 1850s. By 1860, he was working as a machinist apprentice. He received a commission as a captain in Company D of the 34th Massachusetts Infantry in 1862. He was killed in action at the Third Battle of Winchester on September 19, 1864.