He married Phebe Mitchell and their daughter, Phebe Gelston (1771–1836) later married Nicoll Floyd, the son of William Floyd.
As the American Revolution approached, Gelston became politically active. He signed the articles of association in 1774, agreeing to avoid British imports, even though this hurt his own business. He represented Suffolk County in the New York Provincial Congress of 1775 to 1777, as well as the 1777 New York State Constitutional Convention that debated and enacted the first constitution of the State of New York.
He was a member from Suffolk County of the New York State Assembly from 1777 to 1785. During his last term, he was Speaker. As speaker, he took a leading role in reconciling the differences between Tory and Whig factions. He oversaw the repeal of all the laws that had imposed civil and legal penalties on Tories.
In 1787, he removed to New York City, and from 1787 to 1801, was Surrogate of New York County. In 1789, the State Assembly appointed him a delegate to the last session of the Continental Congress. He was a member of the New York State Senate from 1791 to 1794, and from 1798 to 1802.
He was buried in the First Presbyterian Church Cemetery in New York.
- David Gelston at the Biographical Directory of the United States Congress
- The New York Civil List compiled by Franklin Benjamin Hough (pages 114f, 117f, 141, 275 and 415; Weed, Parsons and Co., 1858)
|Speaker of the New York State Assembly
John Lansing, Jr.
|Collector of the Port of New York