James Chestnut, Jr. was born to James Chesnut, Sr. (19 February 1773-17 February 1866) and Mary Bowes Cox (22 March 1775-13 March 1864) near Camden, Kershaw District, South Carolina on 18 January 1815. He attended College of New Jersey (now Princeton University) in Mercer County, New Jersey and graduated with honors from its school of law in 1837. He was admitted to the bar the same year, and established his practice in Camden, Kershaw District, South Carolina. He married Mary Boykin Miller (31 March 1823-22 November 1886) on 23 April 1840. She was the daughter of former South Carolina Governor Stephen Decatur Miller (08 May 1787-08 March 1838), but is best remembered for her wartime personal journal, which was originally published under the title Diary from Dixie in 1905.

     In 1842, he was elected to the South Carolina legislature, serving until 1854 in the House of Representatives, then four years in the Senate (1854-1858). He was also a delegate to the convention of the Southern states in Nashville, Davidson County, Tennessee (03-12 June 1850). When U.S. Senator Josiah James Evans (27 November 1786-06 May 1858) died, he was elected to fill the vacancy and served from 03 December 1858, until 10 November 1860 when he withdrew in support of secession. Like Robert Mercer Taliaferro Hunter (21 April 1809-18 July 1887), the U.S. Senate expelled him in absentia on 11 July 1861.

     Chesnut was a delegate to the South Carolina Secession Convention and subsequently a deputy to the Provisional Confederate Congress. In the second body, he was one of the framers of the Permanent Confederate Constitution, and served on the Naval Affairs and Territories committees. Simultaneously, he served as a colonel and aide on the staff of Brig. Gen. (later Gen.) Pierre Gustave Toutant Beauregard (28 May 1818-20 February 1893). Before the bombardment of Fort Sumter (12-13 April 1861), he and Capt. (later Lt. Gen.) Stephen Dill Lee (22 September 1833-28 May 1908) bore to U.S. Maj. (later Brig. Gen.) Robert Anderson (14 June 1805-26 October 1871) the formal demand to surrender the garrison. Prior to the Battle of First Manassas (21 July 1861), he was dispatched to Richmond to present Beauregard's potential plans to the President.

     With his Congressional term expired and Beauregard transferred, President Jefferson Davis (03 June 1808-06 December 1889) appointed Chesnut his Aide de Camp, with the rank of Colonel of Cavalry, on 19 April 1862. Wishing for a field assignment, he was promoted to Brigadier General on 23 April 1864, and took command of Reserve Forces of South Carolina on 30 April 1864. He continued to operate in Department of South Carolina, Georgia and Florida, until surrendered as part of the Bennett (Bennitt) Place accords of 26 April 1865. Following the war, he resumed his law practice in Camden, Kershaw County, South Carolina, worked to end carpetbagger rule in his state, and was a delegate to the 1868 Democratic National Convention in New York City. Chesnut died 01 February 1885 at Mulberry, his estate near Camden, and is buried in his family's section in nearby Knight's Hill Cemetery.