Harry Flood Byrd, Sr. (June 10, 1887–October 20, 1966) of Berryville in Clarke County, Virginia was an American newspaper publisher, farmer and politician. He was a descendant of one of the First Families of Virginia. His ancestors included William Byrd II of Westover Plantation, who established Richmond, Robert "King" Carter, a colonial governor, and Pocahontas, and he was the brother of famed aviator Richard Evelyn Byrd.

Byrd was a dominant figure in Virginia Democratic Party politics for much of the first half of the 20th century. He became a Governor of Virginia in the mid-1920s and continued to lead a political faction that became known as the Byrd Organization as he represented Virginia as a United States Senator from 1933 until 1965.

Financial conditions in Virginia during his youth conditioned his thinking on fiscal matters throughout his life. He is best remembered for his austere pay-as-you-go financial policies, and dissuasive positions against racial desegregation of the public schools, advocating a policy of massive resistance that led to closure of some public school systems in Virginia in the early 1960s.