Sir Horace Curzon Plunkett was born on October 24, 1854, in Sherborne, Gloucestershire, England.

He was an agricultural reformer and politician. After the death of his mother in 1858, the family moved to his father’s hereditary home, Dunsany Castle in Ireland. He was educated at Eton College and University College, Oxford. He returned to Dunsany Castle, where he acted as agent for his father. In 1879, after the threat of tuberculosis, Plunkett moved to a drier climate in the Rockies of Wyoming, where he took up cattle ranching until the late 1880s. Together with a substantial fortune, he acquired experience that proved invaluable in agricultural education, improvement, and development. He returned to Ireland in 1889 and devoted himself to the agricultural cooperative movement, first organizing creameries and then, in 1894, the Irish Agricultural Organization Society. A moderate Unionist Member of Parliament for South County Dublin in the House of Commons of the UK from 1892 to 1900, he became Vice President of the new Department of Agriculture and Technical Instruction for Ireland (1899–1907). He believed in the independence of Ireland without partition inside the Commonwealth, and he fought strongly for this goal as Chairman of the Irish Convention (1917–1918) and, in 1919, as a founder of the Irish Dominion League. He was appointed to the first Senate of the Irish Free State (1922–1923). Plunkett was knighted in 1903 and elected a Fellow of the Royal Society in 1902 and the Royal Irish Academy in 1929. He received honorary degrees from the Universities of Oxford (1906) and Dublin (1908) and was elected an honorary Fellow of University College, Oxford, in 1909.

He died unmarried on March 26, 1932, in Weybridge, Surrey, England.