Major-General Thomas Harrison, baptised 16 July 1616, executed 13 October 1660, was a prominent member of the radical religious sect known as the Fifth Monarchists, and a soldier who fought for Parliament and the Commonwealth in the Wars of the Three Kingdoms. One of those who approved the Execution of Charles I in January 1649, he was a strong supporter of Oliver Cromwell before the two fell out when The Protectorate was established in 1653. Following the 1660 Stuart Restoration, he was arrested, found guilty of treason as a regicide, and sentenced to death. He was hanged, drawn and quartered on 13 October 1660, facing his execution with a courage noted by various observers, including the diarist Samuel Pepys.

The Fifth Monarchists, or Fifth Monarchy Men, were a Protestant sect which advocated Millennialist views, active during the 1649 to 1660 Commonwealth of England. Named after a prophecy in the Book of Daniel that Four Monarchies would precede the Fifth or establishment of the Kingdom of God on earth, the group was one of a number of Nonconformist sects that emerged during the Wars of the Three Kingdoms. Perhaps its best known adherent was Major-General Thomas Harrison, executed in October 1660 as a regicide, while Oliver Cromwell was a sympathiser until 1653.