A disabled veteran of the Mexican–American War, he worked in family businesses, including as the jailor at Nathan Bedford Forrest's slave pen in downtown Memphis.

[b] A letter to the Natchez Daily Courier described the conditions unfavorably, comparing it to a slave ship:[18] Putting us on board that filthy barque was one of the greatest outrages ever practiced upon soldiers.

and oppressed by petty tyrants, dressed up in a little brief authority: and I write this that all who feel any interest in the Mississippi Battalion, may have an opportunity of forming an opinion of an officer whose duty it was (and who had the means at his disposal) of transporting volunteers—American volunteers in the service of their country to their port of destination in comparative comfort and safety, and who willfully refused to do it when informed of the capacity and condition of the vessel, but crowded us like slaves in a slave-ship, in a vessel so filthy as to endanger the health of all on board.

[22] On June 27, the Vicksburg Daily Whig described Tampico as an unhealthy place as evidenced by the sickly look of the returning soldiers of the Mississippi Battalion.

[3] On March 8, 1849, Forrest submitted an affidavit to the commissioner of pensions in Washington, D.C., recapitulating the dates of his military service and swearing that the surgeon's certificate of disability had been lost.

[24] On June 16, 1849, the pension department notified J. R. Connelly, of Hernando, De Soto County, Mississippi, that Forrest, claimant number 61430, had been issued 160 acres of land.

[21][26] Nathan Bedford Forrest's five younger brothers, including John, were "ideal junior partners" who contributed to a "building a formidable slave-trading operation.

"[27] According to historian Frederic Bancroft in Slave-Trading in the Old South (1931), "By 1860, Forrest had demonstrated what success an...energetic man could achieve in a few years by buying and selling slaves instead of beasts and real estate.

"[28] Bancroft wrote that "According to references during the Bolton trial, John (a cripple from a wound received in the Mexican War) and William were associated with N. B. F. in slave-trading as early as 1857.

[31] As of the late 1920s a Grenada resident named Lida Owens held a bill of sale for "Susan, 17 years old of dark copper color, slave for life" sold by N. B. Forrest on July 28, 1859 to Mrs. H. A.

"[32] Per the anonymous correspondent writing from East Tennessee:[33] The slave pen of old Bedford Forrest, on Adams street, was a perfect horror to all negroes far and near.

Women were often stripped naked with a bucket of salt water standing by, in which to dip the instrument of torture, a heavy leather thong, their backs were cut up until the blisters covered the whole surface, the blood of their wounds mingling with the briny mixture to add torment to the infliction.

On June 11, 1862, while inebriated, John Forrest shot a master's mate of the USS Carondelet named Theodore S. Gillmore while both were present at a facility operated by sex worker Puss Pettus on Main Street in Memphis.

[44] Per the Chattanooga Rebel, "After having been kept in irons for several weeks, he was put into a wooden box, but little longer than his body, bored with holes, barely sufficient to admit the necessary are [sic] to sustain life.

In this condition he was transferred to the most heated part of one of their gunboats, lying opposite the city, where he was fed on bread and water and steamed to the utmost extent of his endurance.

"[45] According to the Memphis Daily Union Appeal of July 4, "The United States naval officer who was shot by John Forrest, has expressed, in epistolary form, a strong desire to have him released from confinement, saying, that he forgave him, freely and pitied him much for his ill health and other infirmities.

"[50] A history of the Carondelet lists Gillmore as a crewman and describes his participation in the Battle of Island Number Ten but makes no mention of John N.