James Duane established a New York law practice after admission to the bar in 1754. His colonial employment included work in chancery and public legal business. Although cautious about the break with Britain, he joined the revolutionary movement and represented New York in the Continental Congress. He participated in the long process of framing the Articles of Confederation and served on committees concerned with finance, military affairs and relations with Indigenous nations.

After the British evacuation, Duane became New York City's mayor in 1784. He helped restore municipal government and also presided over the Mayor's Court. In Rutgers v. Waddington, a dispute over property occupied during the war, the court limited the application of a state trespass statute by considering the law of nations and the peace settlement. The judgment drew criticism from opponents who wanted stronger remedies against those associated with British occupation.

Duane also served in the state Senate and supported the new federal Constitution. In September 1789 George Washington nominated him as the first judge of the United States District Court for New York. He held that office until resigning through ill health in March 1794. Landownership and development remained substantial interests, including the settlement that became Duanesburg. His legal papers and journals document colonial practice, revolutionary politics and municipal government. He died in 1797.