John Jones Pettus (October 9, 1813 – January 25, 1867) was an American politician, lawyer, and slave owner who served as the 23rd Governor of Mississippi, from 1859 to 1863. Before being elected in his own right to full gubernatorial terms in 1859 and 1861, he served as acting governor from January 5 to 10, 1854, following the resignation of Henry S. Foote. A member of the Democratic Party, Pettus had previously been a Mississippi state representative, and a member and president of the Mississippi State Senate. He strongly supported Mississippi's secession from the United States and brought his state along as a founding member of the Confederate States of America in 1861. Pettus's term of office came to an end in 1863, the same year that saw much of Mississippi overrun by Union forces. At the close of the war he fled to Arkansas to avoid prosecution and died there in 1867.

John Jones Pettus was born on October 9, 1813, in Wilson County, Tennessee, to John Pettus, a farmer, and his wife Alice Taylor (née Winston) Pettus. He was the brother of Edmund Pettus, and a distant cousin of Jefferson Davis. He was raised in Limestone County, Alabama, after his father moved the family from Tennessee. Only nine when his father died, Pettus helped with chores and was educated at home by his mother. Pettus settled in Mississippi in 1835. After a brief stay in Sumter County, Alabama, where he studied law, he opened a law practice in Scooba, Mississippi. In the 1840s, he married a cousin, Permelia Winston. He became a farmer and by 1850 owned 1,600 acres (647 ha) and enslaved twenty-four people. Permelia died in 1857 and Pettus married Sarah H. Potts, of Tuscaloosa, Alabama in 1861. During the Civil War, Pettus's son John joined one of the Mississippi regiments in Virginia and was killed at the Battle of Ball's Bluff in October, 1861.

In 1844, Pettus represented Kemper County in the Mississippi House of Representatives. In 1848, he was elected to the Mississippi Senate. In 1853, while Governor Henry S. Foote was waiting for the January 11 inauguration of John J. McRae, Foote grew bitter and angry, addressing the legislative session by announcing that he had considered resigning in protest once the election results came in. At noon on January 5, 1854, Foote's resignation was received by the state senate.

The Mississippi Constitution of 1832 had abolished the office of lieutenant governor. As President of the Mississippi Senate, Pettus was next in seniority and sworn in at noon on January 7, 1854. He held the governorship until McRae was sworn in on January 10, 1854. His only recorded act during these 120 hours was to order a special session in Noxubee County to fill the office of a deceased state representative, Francis Irby. On January 11, McRae was inaugurated as governor, and Pettus returned as senate president. During the 1850s, he became identified as "the Mississippi Fire-eater," a term referring to Southerners supporting secession. As a state senator, Pettus developed a reputation as a "disunion man of the most unmitigated order", advocating for Mississippi delegates to attend the Nashville Convention and discuss the possibility of secession during the 1850 political crisis.

In 1859, Pettus was elected governor by a 3-1 margin. In his inaugural address, he said that the South's only way to maintain slavery was secession and a Southern Confederacy, and he pledged to defend the "superiority and supremacy of the white race" against "Black Republicans". Following President Abraham Lincoln's election, on November 26, 1860, Pettus called for a special session of the state legislature and advocated for a convention to withdraw Mississippi from the United States. The legislature voted to hold a Secession Convention which convened in Jackson on January 7, 1861. Two days later, the state officially declared its withdrawal from the US. On February 4, 1861, Mississippi along with other slave states formed the Confederate States of America, precipitating the American Civil War.

With the outbreak of the Civil War, Pettus was faced with numerous challenges, first and foremost being the military situation. While large numbers of volunteers began organizing themselves into military companies immediately after the 1860 Presidential election, Mississippi lacked the funds and arms to supply them. Mounting frustration developed between the Confederate government and Mississippi regarding manpower, because the state took the position that regiments should only be transferred to Confederate service once fully armed. Although some regiments were outfitted at private expense and mustered into the Confederate Army, the state legislature did not supply sufficient funds to buy weapons and lacked existing arsenals to supply the volunteers. To minimize the number of unequipped troops with nothing to do, Pettus instituted a moratorium on volunteer enlistments in May 1861 until the existing units could be properly armed.

Some of the Mississippi volunteer regiments were sent to Virginia to join the Confederate Army, while others remained in the service of the state and were sent to the Gulf Coast during the Pensacola campaign to besiege Federal forts and resist any attempt at a coastal invasion. Mississippi troops occupied Ship Island to take control of its strategic deep water port, but Union gunboats forced them off the island in September 1861. Ship Island remained under Union control for the rest of the war, serving as a base for the capture of New Orleans and raids on the Mississippi coast.

In response to a call for aid from Confederate forces in Kentucky, on September 28, 1861 Governor Pettus asked for 10,000 volunteers to enlist in state's armed forces. The legislature voted funds to pay for this force, deemed the "Army of 10,000", but only authorized a 60-day term of service and did not provide weapons. Before even half of the quota of 10,000 men could be filled, the troops were sent north with inadequate supplies and training. The volunteers in Kentucky did not see combat, but they were exposed to severe winter weather and outbreaks of disease before returning to Mississippi at the end of January 1862.