Samuel Greene Arnold, Jr. (April 12, 1821February 14, 1880) was a United States Senator from Rhode Island. Born in Providence, Rhode Island, he received his early education under private tutors, and graduated from Brown University in 1841 and, in 1845, the law department of Harvard University, gaining admission to the bar that year. He was a lawyer and historian, and was trustee of Brown University from 1848 to 1880.