George Robertson Dennis (April 8, 1822 – August 13, 1882), a Democrat, was a United States Senator from Maryland, serving from 1873 to 1879. He also served in the Maryland State Senate and the Maryland House of Delegates.

Dennis was born in Whitehaven, Maryland to Maria (née Robertson) and John Upshur Dennis. His brother was James U. Dennis.^{[1][citation needed]} His half-brother was Samuel K. Dennis.^[2] He graduated from Rensselaer Polytechnic Institute in Troy, New York. He entered the University of Virginia at Charlottesville, and studied medicine at the University of Pennsylvania School of Medicine in Philadelphia. He graduated in 1843 and practiced in Kingston, Maryland, for many years, until later devoting himself to agricultural pursuits.

In 1854 and 1871, Dennis served as a member of the Maryland State Senate, and in 1867 served in the Maryland House of Delegates. He was elected as a Democrat to the United States Senate and served from March 4, 1873, until March 3, 1879.

He died in Kingston in 1882, and is interred in St. Andrew's Churchyard of Princess Anne, Maryland.