Born probably in Saint John"s, Newfoundland in April 1740, he moved to New York City in early youth and engaged in mercantile pursuits. He served in the New York State Assembly from 1784 to 1787 and in the New York State Senate from 1798 to 1808. Denning was elected as a Democratic-Republican to the Eleventh United States Congress, beginning on March 4, 1809, but never took his seat, and eventually resigned in 1809 or 1810.
He died in New York City in 1819.
Interment was in Saint Paul"s Churchyard.
He was a member of the Committee of One Hundred in 1775, was a delegate to the New York Provincial Congress from 1775 to 1777 and was a member of the convention of State representatives in 1776 and 1777. He was a member of the Council of Appointment in 1799.