Thomas Plumer Halsey MP (26 January 1815 – 24 April 1854) was a Member of Parliament for Hertfordshire from 1846 to 1854.
He was the son of Joseph Thompson Whately (d. 1818), who, on his marriage in 1804 to Sarah, the only child of Thomas Halsey MP, assumed that surname by Act of Parliament.
Thomas Plumer Halsey was elected Member of Parliament for Hertfordshire unopposed in January 1846 following the elevation of the previous incumbent, James Grimston to the House of Lords.
On 23 January 1839, he married Frederica, the only child of General Frederick Johnston, at Marylebone. Halsey, his wife and his infant son, Ethelbert Arthur Sackville Halsey, were drowned in the shipwreck of the steamer Ercolano in the Gulf of Genoa, along with 13 other English passengers. Fellow passenger Sir Robert Peel survived by swimming. The older son, Frederick Halsey, survived as he was a pupil at Eton at the time. He went on to become the 1st of the Halsey Baronets.