Born in Lancaster County, Pennsylvania on August 15, 1844, Thomas Watson later moved with his family to Stevenson County, Illinois, where they engaged in farming and stockholding. Watson enlisted in Company D of the 93rd Illinois Infantry at Adeline, Illinois, on August 7, 1862, during the American Civil War. He trained with the regiment at Fort Douglas, Illinois, and participated in Grant's Vicksburg Campaign and Sherman's Atlanta Campaign. Watson mustered out with the regiment on June 23, 1865 at Louisville, Kentucky. In the final letter within this collection, written in 1866, Watson expresses an intent to settle in Macon City, Missouri. By 1869, however, he was in Freeport, Illinois, where he married Lydia Amelia Sheller. An 1898 regimental history indicates that Watson was living in Kansas in the late 19th century. Some time later, the family moved to Olympia, Washington, where Watsson lived until his death on May 23, 1927. He is bured in the Masonic Memorial Park Cemetery of Tumwater, Washington.

The 93rd Illinois Infantry was organized at Chicago and mustered into service on October 13, 1862. The regiment participated in Grant's Vicksburg Campaign and Sherman's Atlanta Campaign. The 93rd was mustered out of service in Kentucky on June 23, 1865.