Harmar Denny (May 13, 1794 – January 29, 1852) was an American businessman and Anti-Masonic member of the U.S. House of Representatives from Pennsylvania.
Harmar Denny was born in Pittsburgh the son of Ebenezer Denny and Nancy Wilkins. Graduating from Dickinson College in Carlisle in 1813, he then practiced law in Pittsburgh. He served as a member of the Pennsylvania State House of Representatives from 1824 to 1829.
Denny was elected as an Anti-Masonic candidate to the Twenty-first Congress to fill the vacancy caused by the resignation of William Wilkins. He was reelected to the Twenty-second through Twenty-fourth Congresses and served from December 15, 1829, to March 3, 1837. After his term, he resumed the practice of law in Pittsburgh, and became a delegate to the Pennsylvania State Constitutional Convention in 1837. He was a presidential elector on the Whig ticket in 1840. As commissioner under act of incorporation of the Pennsylvania Railroad Company, April 13, 1846, he incorporated the Ohio & Pennsylvania Railroad Company, 1848. He declined the nomination to be a candidate for Congress in 1850. He served as president of the Pittsburgh & Steubenville Railroad Company in 1851 and 1852. He was a trustee of the Western University of Pennsylvania, now the University of Pittsburgh, and director of the Pittsburgh Theological Seminary.
Harmar Denny was the great-grandfather of Congressman Harmar D. Denny, Jr. of Pennsylvania.
He is buried at Allegheny Cemetery in Pittsburgh's Lawrenceville neighborhood.