Isaac Roosevelt (December 19, 1726 - October 1794) was an American merchant andFederalist politician. He served in the New York State Assembly and the state Constitutional Convention and achieved the most political success of any Roosevelt before Theodore Roosevelt. He was the great-great-grandfather of the U.S. PresidentFranklin Delano Roosevelt.

Roosevelt was born in New York City and baptized in the Reformed Dutch Church of New York. A member of the Roosevelt family, he was the son of Jacobus Roosevelt, grandson ofNicholas Roosevelt, and great-grandson of the immigrant Claes Maartenszen Van Rosenvelt.

He was one of the first large-scale sugar refiners in New York City. He built one of the first sugar refineries in the city and originally had his store on Wall Street, later removing to St. George's Square.

"Isaac Roosevelt is removed from his house in Wall Street to the house of his late brother, Jacobus Roosevelt, Jr, deceased, near the Sugar house, and opposite to Mr. William Waltons, being on the northwest side of Queen Street, where his customers may be supplied as usual with double, middling and single refined loaf sugars, clarified, muscovado and other molasses, & etc." - April 25, 1772
Active in the community, he was one of the first members of the New York City Chamber of Commerce, organized in 1768, and he was one of the original incorporators of the first public hospital in New York in 1770. He was a cofounder of the Bank of New York in 1784, and became its second president, a post he held from 1786 to 1791.

A noted Whig, he was elected to the New York Provincial Congress on April 22, 1775. He was one of the Committee of One Hundredthat took control of the state government in May 1775. Though he felt no allegiance to England, he was initially a moderate, hoping to prevent conflict. However, he withdrew from New York when the British occupied the city, and spent the period of occupation at his wife's home in Dutchess County, serving with the Sixth Regiment of the Dutchess County Militia. After the war, as one of ten representatives from New York City (among John Jay, Alexander Hamilton, and Robert R. Livingston), he took part in the New York State Convention at Poughkeepsie on June 18, 1788 that deliberated on the adoption of the United States Constitution. He was a member of the New York State Senate (Southern D.) from 1777 to 1786, and from 1789 to 1792.

He married Cornelia Hoffman, the daughter of a prominent Dutchess County landowner, on September 22, 1752. They had ten children, including Jacobus (James), great-grandfather of Franklin Delano Roosevelt. He died in October 1794.