William Henry Thomas was born on June 12, 1845, in Hingham, Massachusetts, to Benjamin and Sally Thomas. His father was a blacksmith who owned $2,500 of real estate by 1850. He grew up and attended school in Hingham, and his father probably died in the 1850s.
He enlisted in the Union army, and he mustered in as a private in Company A of the 32nd Massachusetts Infantry on October 31, 1861. He apparently lied about his age, claiming that he was 18 years old.
He fell ill in the fall of 1862 and spent several months recovering. He fell ill again with chronic diarrhea in the spring of 1863, and army officials transferred him to the 78th Company, 2nd Veteran Reserve Corps Battalion in August 1864. He mustered out on November 25, 1864.
He returned to Hingham after leaving the army, and he married Mary W. Higgins on October 30, 1867. They had at least two children: Harry, born around 1871; and Helen, born around 1877. He worked as a house painter, and by 1870, he owned $150 of real estate and $200 of personal property. By 1900, he was working as a superintendent at the Hingham Water Works.
He served as secretary of his regimental veterans’ association, and a local writer described him as a “prominent G.A.R. [Grand Army of the Republic] man.” He died of heart disease in Hingham on February 28, 1911.