On Friday 3 September 1658 Oliver Cromwell died unexpectedly at Whitehall. Although he had been ill, his illness was not believed to be mortal. But on the night of 17 August he was once again bedridden with severe pains and on 24 August Secretary John Thurloe reported to Henry Cromwell that his father had fallen into fits. Even by then, Thurloe, one of Cromwell's inner circle, reported that “the doctors do not conceive there is any danger to his life.” No provision had yet been made for the succession and ministers were still confidently thanking God for his recovery when on 2 September the Council of State attempted to have Cromwell name his successor. By then Cromwell was largely comatose, unable to speak, and the attempt failed. The Council members claimed they put his eldest son Richard's name to him and Cromwell gave a sign of assent, either a nod or a whispered yes. When Cromwell finally died, Richard was immediately proclaimed protector.

Not the most rational choice for a successor, Richard was perceived as less capable – certainly he was less experienced in public affairs – than his brother Henry, at the time Lord Deputy of Ireland. A contemporary observer, the puritan Lucy Hutchinson, wrote that Cromwell's “army and court [substituted] his eldest son, Richard, in his room, who was a meek, temperate, and quiet man, but had not a spirit fit to succeed his father, or to manage such a perplexed government.”