Archibald Leitsh Gillis was born on August 22, 1830, in Barnet, Vermont, to John Gillis and Mary Leitsh. By 1850, he was working as a laborer in Danville, Vermont. He married Martha E. Jones around 1852, and they had at least six children: Florence, born around 1857; George, born around 1859; Martha, born around 1862; John, born around 1868; Coburn, born around 1871; and Belle, born around 1872.
He enlisted in the Union army on September 25, 1861, and he mustered in as a corporal in Company E of the 6th Vermont Infantry on October 15. The regiment took part in the Battle of Antietam, the Battle of Fredericksburg, the Battle of Chancellorsville, the Battle of Gettysburg, the Overland Campaign, and the siege of Petersburg. He acted as a hospital steward during the war, and he was eventually reduced to the ranks for an unspecified offense. He mustered out on October 28, 1864.
He settled in Burke, Vermont, after the war, and he worked as a farmer. By 1870, he owned $2,000 of real estate and $803 of personal property. They moved to Danville, Vermont, in the 1870s. His wife died in 1891. By 1900, he was living in Peacham, Vermont. A local writer declared him a “highlight respected citizen and Christian gentleman.” He died of arteriosclerosis in Caledonia County, Vermont, on June 8, 1911.