David Hartley Armstrong (October 21, 1812 – March 18, 1893) was a United States senator from Missouri.

Born in Nova Scotia, British Canada, he attended Maine Wesleyan Seminary and taught school in New Bedford, Massachusetts from 1833 to 1837.

Armstrong served as a member of the board of freeholders which framed the charter of St. Louis in 1876, and was appointed as a Democrat to the U.S. Senate to fill the vacancy caused by the death of Lewis V. Bogy, serving from September 29, 1877, to January 26, 1879, when a successor was elected and qualified.

Armstrong was Vice President of the St. Louis Board and helped command the July 27, 1877 cavalry attack on the strikers outside Schuler Hall, the headquarters of the Executive Committee coordinating the St. Louis General strike.

He reportedly yelled from a shady side of the street for his policemen to "Ride 'em down!".