Robert Poore Haythorne was born 2 December 1815 at Clifton, Bristol, England, to John Haythorne and Mary Curtis. R. P. immigrated to Prince Edward Island at the age of 25 to join his brother Edward Curtis Haythorne who was a landowner in the Marshfield area of Lot 34. R. P. and his brother held 10,000 acres of land which included their farm and portions leased to tenants under the standard lease agreement of 999 years.

R. P. married Elizabeth Radcliffe Scott, daughter of Thomas Scott, on 28 May 1861. The couple had two children: Edward Curtis (b. 1862) and Thomas Joseph (b. 1863). Elizabeth died in Liverpool in September 1864 while traveling to visit family in Belfast, Ireland.

Tension between proprietors and tenants were running high in PEI the 1860s. R. P. had a progressive view of the so-called “land question” and by 1866 had sold his estate to tenants and squatters for $2 an acre. This move made him popular among tenants across the Island and R. P. was elected to the Legislative Council for 2nd Queens in 1867. When J. C. Pope’s government resigned, R. P. was asked to join the cabinet of Premier George Coles. Joseph Hensley succeeded Coles and when Hensley took a position at the Supreme Court, R. P. found himself Premier. Some of the key issues during R. P.’s term included the question of Confederation, land issues, and development of an Island railway. R. P. resigned in 1870 due to lack of support in the Assembly but was back in power in 1872. After committing to extending the railway to both the eastern and western ends of the Island, R. P. entered into negotiations to bring PEI into Confederation. R. P. lost to Pope in the 1873 election.

R. P. was appointed to the Senate in 1873 and held the position until his death in May 1891. R. P. Haythorne is buried in Ottawa, Ontario.