During the War of 1812, he served as assistant adjutant general of the New York Militia, under Major General Ebenezer Stevens. After the war, he opened a commission house in New York City with his father-in-law, Archibald Gracie, under the name James G. King and Company. Three years later in 1818, he moved to Liverpool, England and established King & Gracie with his brother-in-law, Archibald Gracie Jr., where he established "a high reputation for business ability, and, despite the sever financial crisis of 1822, 1823, and 1824, was able to meet all his obligations and to finally close up the affairs of his house on a satisfactory basis." While in Liverpool, he met and eventually became a close friend of John Jacob Astor, who offered him the presidency of the American Fur Company, which King declined. In 1824, he returned to New York City and engaged in banking as a partner in the firm of Prime & Ward, with residence in Weehawken, New Jersey. In 1835, he succeeded Eleazar Lord to become president of the Erie Railroad, although he did not collect a salary. He served until 1837, when by his visit to London he secured the loan to American bankers of $1,000,000 from the governors of the Bank of England.
In 1834, he was a candidate for Congress in New York City, but was defeated. King was elected as a Whig to Congress, succeeding fellow Whig Dudley S. Gregory, the former mayor of Jersey City. He served alongside his older brother John in office from March 4, 1849 to March 3, 1851, but declined to be a candidate for renomination in 1850 and was succeeded by Democrat Rodman M. Price. While in Congress, he was a member of the Committee of Commerce, and he opposed the repeal of the Missouri Compromise and the Fugitive Slave Act of 1850. Upon the ascendancy of Millard Fillmore to the presidency after Zachary Taylor's death in 1850, King was reportedly considered for United States Secretary of the Treasury, but informed Fillmore that he did not wish to serve as he had planned on retiring from public service and was, in fact, leaving Congress at the end of the term.
Later career
After leaving Congress, he resumed the banking business. By this time the firm he had worked for had undergone dissolution, and so was succeeded by the House of James G. King & Son.
Personal life
On February 4, 1813, King was married to Sarah Rogers Gracie, the daughter of Archibald Gracie, a Scottish-born shipping magnate and early American businessman and merchant in New York City and Virginia. Together, they were the parents of eleven children, many of whom married into prominent colonial families, including:
James Gore King, Jr., who married his first cousin, Caroline King, a daughter of John Alsop King.
Archibald Gracie King, who married Elizabeth Denning Duer, a daughter of William Alexander Duer.
Mary King, who married Edgar Henry Richards in 1856.
Frederika Gore King, who married Bancroft Davis, an American lawyer, judge, diplomat, and president of Newburgh and New York Railway Company.
Edward King, who married Isabella Ramsay Cochrane in 1858. After her death, he married Elizabeth Fisher.
Fanny King, who married James Latimer McLane, brother of Robert Milligan McLane, in 1859.
King died of a "congestion of the lungs" on October 3, 1853 at his country place, "Highwood," near Weehawken, New Jersey, which he had purchased in 1832. He was interred in the churchyard of Grace Church, Jamaica, New York.
