John Tompkins Gwyn was born on July 25, 1834, in Freeport, Virginia, to Charles and Mary Gwyn. He grew up in Gloucester County, Virginia, and he married Mary C. Thurston there on December 23, 1858. They had at least five children: Mary Grace, born around 1859; Laurence, born around 1865; Lucy, born around 1869; Fannie, born around 1871; and Matthew, born around 1876. Gwyn worked as a farmer in Gloucester County.
He enlisted in the Confederate army on April 23, 1861, and mustered in as a 2nd lieutenant in Company G of the 26th Virginia Infantry on June 4. The regiment took part in the Seven Days Battles and helped defend Charleston, South Carolina, and then Petersburg, Virginia. He was wounded in the left arm on June 15, 1864, during the Siege of Petersburg, and Confederate officials sent him home to recover. He rejoined his regiment by October 1864, and he eventually received a promotion to 1st lieutenant. He was wounded again in the spring of 1865, and Confederate forces left him in a Richmond hospital when they evacuated the city. He was captured on April 3, 1865.
Gwyn returned to Gloucester County after the war, but the family moved to Baltimore, Maryland, soon afterward. By 1870, he was working as a clerk, and he owned $750 of real estate and $300 of personal property. His wife Mary died in Baltimore on February 16, 1897, “after a long and painful sickness.” Gwyn moved into his son Matthew’s household in Chicago, Illinois, soon afterward, and he died there on February 26, 1900.