John Hailstock was born around 1834 in Charlottesville, Virginia. Little is known about his life before the war except that he lived in Charlottesville, worked as  a farmer, and was married at the time of his enlistment. 

On June 14, 1863, at the age of 29, Hailstock enlisted and mustered into the Union army at Mason's Island, Virginia (now known as Theodore Roosevelt Island near Washington, D.C.). His service record describes him as 5 feet, 8 1/4 inches tall, with black hair, black eyes, and a black complexion. He served in Company D of the 1st USCT Infantry Regiment. During his time with the 1st USCT, Hailstock took part in numerous key operations throughout Virginia and North Carolina. The army assigned the regiment to duty at Norfolk, Portsmouth, and Yorktown, Virginia, until April 1864, during which time they participated in the Richmond-Petersburg Campaign. The regiment was present for the mine explosion in front of the Confederate line, which resulted in the Battle of the Crater on July 30. The men also saw action at the Battle of New Market Heights at Chaffin’s Farm on September 28-30. Hailstock, however, was then sick in hospital during August 1864. In December, the regiment carried out an expedition to Fort Fisher, North Carolina, which resulted in the fall of the fort on January 15, 1865, and the subsequent shuttering of the Confederacy's last true maritime port in Wilmington. The regiment advanced into North Carolina, occupying Goldsboro in March and Raleigh in April. It was present at the surrender of General Joseph E. Johnston on April 26, the largest, and one of the last, Confederate surrenders. The 1st USCT was assigned to duty in the Department of North Carolina until September. Hailstock mustered out on September 29, 1865, on Roanoke Island near the Outer Banks.

Following the war, Hailstock lived in Pennsylvania, primarily in the towns of Milton and Watsontown. He suffered from piles and rheumatism following his service. He began receiving a pension of $12 per month in 1890. Hailstock died March 15, 1910, of unknown causes somewhere in Virginia.