Hardin was only 12 years old when members of the Confederate Army returned home after the American Civil War. The war had a powerful impact on Hardin and he developed a strong hatred of the freed slaves and killed his first black man when he was 15 years old. Hardin fled from home after the killing. As he was later to explain: "To be tried at that time for the killing of a Negro meant certain death at the hands of a court backed by Northern bayonets... thus, unwillingly, I became a fugitive not from justice, be it known, but from the injustice and misrule of the people who had subjugated the South."
In the next few weeks Hardin was to kill three more men. These were soldiers who had attempted to take him into custody. Hardin moved to Navarro County where he became a school teacher. This was followed by work as a cowboy. He then tried to make a living out of poker but this resulted in him killing Jim Bradley in a gambling row.
Hardin's next killing took place in Kosse, Texas when a man tried to rob him. As he pointed out later: "I told him that I only had about $50 or $60 in my pocket but if he would go with me to the stable I would give him more, as I had the money in my saddle pocket ... He said, "Give me what you have first." I told him all right, and in so doing, dropped some of it on the floor. He stooped down to pick it up and as he was straightening up I pulled my pistol and fired. The ball struck him between the eyes and he fell over, a dead robber."
In 1871 he was involved in taking cattle to Abilene where he met Wild Bill Hickok. Hardin later claimed he "killed five men on the journey and three more at his destination". After killing four black men he was arrested by the sheriff of Cherokee County. He escaped from jail in October 1872, and was soon back in trouble with the law. This included the killing of Charles Webb, deputy sheriff of Brown County, on 26th May, 1874.
Hardin fled to Florida and over the next few months killed six more men. With a $4,000 price on his head Hardin was pursued by several bounty hunters. Eventually he was captured by Captain John Armstrong and a party of Texas Rangers at Pensacola on 23rd July, 1877. The following year he was sentenced to 25 years in prison. He was taken to Huntsville in Texas and he spent his time studying law, theology and mathematics. Hardin regained his religious faith and became superintendent of the Sunday School in prison.
In 1894 Hardin was released from prison. He joined his children in Gonzales County (his wife Jane had died on 6th November, 1892) before moving to Karnes County, where he married Callie Lewis on 8th January, 1895. The marriage was not a success and Hardin moved to El Paso where he worked as a lawyer. Hardin also began writing his autobiography.
Hardin got in trouble in 1895 when he started claiming that he paid Jeff Milton and George Scarborough to kill Martin McRose. Milton and Scarborough were arrested but Hardin later withdrew his comments and the men were released.
His next dispute concerned John Selman. He began saying unpleasant things about Selman's son after he arrested Hardin's girlfriend for vagrancy. On 19th August, 1895, Selman shot John Wesley Hardin in the back of the head while he was standing at the Acme Saloon Bar.
The El Paso police found Hardin's unfinished autobiography in the house he rented in the town. This was handed over to his children and the book, Life of John Wesley Hardin as Written by Himself was published in 1896.