The pattern of his character and the details of his life have to be pieced together from scanty evidence. Of his youth we know almost nothing, beyond the fact that as a subaltern in the New Model Army he had been present at the execution of Charles I in 1649, and subsequently fought the Scots Royalists at the Battle of Dunbar in 1650, and again at Worcester in 1651.
At some point in his life Rumbold lost an eye, though it is unclear if this was a battle injury or not. Because of this disability, and because of his fierceness of spirit, he was known to his friends as Hannibal. He married the widow of a maltster and thus came into possession of Rye House at Hoddesdon, Hertfordshire. After long years of obscurity he emerged as one of the extreme Whig faction at the time of the Rye House Plot, having lost none of his republican radicalism. The plan was to conceal a force of 100 men in the grounds of the house and ambush the King and his brother on their way back to London from the horse races at Newmarket. When the conspiracy was discovered Rumbold fled to Holland, joining other exiled opponents of the Stuarts.
In 1685, after the death of Charles II a plot took shape among the émigrés to dislodge James II, his Catholic successor, from the throne. This was to take the form of a two-pronged attack on the British Isles: the first on Scotland under the leadership of Archibald Campbell, 9th Earl of Argyll; and the second on the west of England under James Scott, Duke of Monmouth.
To emphasise the joint nature of the enterprise Rumbold accompanied Argyll to Scotland, and was eventually given a colonelcy in his small army. He was an able officer, and one of Argyll's most devoted supporters. But the whole enterprise, badly mismanaged, fell apart. Argyll and Rumbold were both captured. Rumbold was executed in Edinburgh on 26 June 1685. Argyll, awaiting his own death, said of him: "Poor Rumbold was a great supporter to me and a brave man and died Christianly."
Hannibal Rumbold made his own defiant declaration on the scaffold:
|“||This is a deluded generation, veiled in ignorance, that though popery and slavery be riding in upon them, do not perceive it; though I am sure that there was no man born marked by God above another; for none comes into this world with a saddle on his back, neither any booted and spurred to ride him...||”|
- A Complete Collection of State Trials, vol. IX, 1816, p. 882.
- Douglass Adair, "Rumbold's Dying Speech, 1685, and Jefferson's Last Words on Democracy, 1826", in The William and Mary Quarterly 3rd Series, 9.4 (October 1952:521–531) p 523f.).