Augustus Smith was born around 1839 in Underhill, Vermont, to Joseph and Sophia Smith. His father was a farmer who owned $12,000 of real estate and $1,650 of personal property by 1860. He grew up and attended school in Highgate, Vermont, and by 1860, he was working as a farmer. He may have moved to New Ipswich, New Hampshire, in the early 1860s.
He enlisted in the Union army on December 23, 1861, and he mustered in as a private in Company M of the 1st New Hampshire Cavalry the following day. The regiment took part in the Second Battle of Bull Run and the Battle of Chancellorsville. He fell ill in May 1862 and spent some time in a hospital. Confederate forces captured him near Middleburg, Virginia, on June 18, 1863. He was paroled and eventually exchanged. He died near Columbia Furnace, Virginia, on October 6, 1864.