John Hays was born in Carlisle, Pennsylvania on February 2, 1837 the youngest of two sons and a daughter of John and Eleanor Blaine Hays. On both sides of his family, the young John Hays was descended from old and highly respected central Pennsylvania stock. He was educated in the common schools of Carlisle and at the Plainfield Academy and entered Dickinson College in 1852. After a time away from his studies, he re-entered the College in 1854 and joined the class of 1857. He was a member of Phi Kappa Sigma and was elected to the Belle Lettres Society. Following graduation with his class, he entered law studies in Carlisle with Robert Henderson.
He was called to the Cumberland County bar in August 1859 and entered practice locally. In August 1862, he was commissioned a second lieutenant and then first lieutenant in the newly raised Company A of the 130th Regiment of Pennsylvania Volunteers. The 130th was one of the undrilled and untrained new regiments thrown into the action that culminated in the battle of Antietam. The unit later fought with heavy losses in the classes at Fredericksburg and Chancellorsville where Hays, now adjutant of the regiment, was wounded in the right shoulder by a musket ball. He also served as adjutant to General William Hays for a time at brigade headquarters of the 2nd Brigade of the Third Division. He mustered out with his regiment on May 21, 1863 and returned to Carlisle, entering Henderson's law firm.
He resumed a long and prestigious local career, serving as president of the Carlisle Deposit Bank, as co-founder and chairman of the Carlisle Manufacturing Company, and a director of the Carlisle Gas and Water Company. He was active in civic and church affairs, as well. A Presbyterian, he was one of the original trustees of the Metzger Institute for Women in Carlisle that his uncle founded. He was also an active Republican and was a delegate to the national convention in 1880 and a presidential elector in the elections of 1904 and 1916. He spoke of his war experiences in later life, publishing his remarks on his old regiment's achievements, and was a local member of the Grand Army of the Republic.
He had married on August 8, 1865, Jane Van Ness Smead, sister of John Radcliffe Smead, and the couple had two sons and two daughters, including Raphael Smead Hays of Dickinson's class of 1894. John Hays died in Carlisle on November 30, 1921. He was eighty-four years old.