Benjamin Say was born in Philadelphia, Pennsylvania, to Thomas (1709–1796) and Rebekah Atkinson Budd Say (1716–1795), He married Ann Bartram Bonsall (1759–1793) on Oct. 1, 1776, a granddaughter of naturalist John Bartram. Their son Thomas Say (1787–1835) became a pioneering entomologist.
Say graduated from the medical department of the University of Pennsylvania at Philadelphia in 1780 and practiced in that city. He also worked as an apothecary. He served in the American Revolutionary War, and was a fellow of the College of Physicians of Philadelphia, of which he was one of the founders in 1787, and was treasurer from 1791 to 1809. He was a member of the Pennsylvania Prison Society and president of the Pennsylvania Humane Society. He was a member of the Pennsylvania State Senate.
Say was elected as a Democratic-Republican to the Tenth Congress to fill the vacancy caused by the resignation of Joseph Clay. He was reelected to the Eleventh Congress and served until his resignation in June 1809. He died in Philadelphia in 1813.
- "Genealogical Records Copied from the Bible of Thomas Say". The Pennsylvania Magazine of History and Biography. XXIX: 219–22. 1905.
- Fisher, George. "Thomas Say". Philadelphia Reflections. Retrieved March 21, 2013.
- Cox, Harold. "Senate Members "S"". Wilkes University Election Statistics Project. Wilkes University.
- "Item: "The Cliffs" Country Residence of Benjamin Say at Gray's Ferry". Digital Library. Historical Society of Pennsylvania. Retrieved February 11, 2016.
- United States Congress. "Benjamin Say (id: S000098)". Biographical Directory of the United States Congress.
- The Political Graveyard
- Plan of Say Burial Ground, at 3rd and Arch Streets in Philadelphia
- Watercolor of grave marker