Thomas Parker was born around 1844 in Charlottesville, Virginia. The details of his life before the war are unknown, but he enlisted in the 23rd USCT Infantry Regiment on April 2, 1864, in Washington, D.C., for a period of three years. At the time of his enlistment, Parker was only 20 years old, and he stood 5 feet, 1 1/12 inches tall, with a black complexion, black hair, and brown eyes. He mustered in the same day as a private in Company G. Parker's regiment was assigned to the 9th Corps of the Army of the Potomac at the beginning of the Overland Campaign in May and June of 1864. During the campaign, the regiment was assigned to guard the wagon trains of the Army of the Potomac through the Wilderness, arriving at Petersburg between June 15-18. 

The men took part in the Battle of the Crater on July 30, 1864. Parker also took part in actions against the Weldon Railroad between August 18-21 and the Battle of Fort Sedgwick on September 28. Page and the regiment continued to help General Ulysses S. Grant forcibly extend General Robert E. Lee's lines west of Petersburg, seeing action in the Battle of Poplar Grove Church on September 29-30, and the Battle of Hatcher's Run on the Boydton Plank Road between October 27-28. Following these actions, the men were transferred to the Bermuda Hundred front on December 13, and they remained there until March 1865.  

During the Appomattox Campaign between March 28-April 9, the regiment saw action at Hatcher's Run on March 29-31. They marched into Petersburg on April 2 and pursued Lee's Army of Northern Virginia between April 3-9. Grant finally caught up to Lee at Appomattox Court House on April 9, 1865, and Parker's regiment was present for Lee's surrender. The army transferred the regiment to Texas soon afterward. Sometime in May, however, Parker was admitted to the hospital at Fortress Monroe, Virginia. He never recovered rejoined his regiment, and the army eventually transferred him to Harewood General Hospital in Washington, D.C. His time in the hospital in the capital marks the end of known records for Parker.