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 severe 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 (later serving as an executor of his will), who offered him the presidency of the American Fur Company, which King declined.