On 16 December 1653, Oliver Cromwell was formally installed as Lord Protector of the Commonwealth of England, Scotland and Ireland. This significant constitutional transition followed the dissolution of the Rump Parliament and the subsequent failure of the Nominated Assembly, often referred to as the Barebone's Parliament. By accepting the Instrument of Government, the first written constitution of England, Cromwell assumed the role of head of state, effectively establishing the period of the Protectorate.

The implementation of the Instrument of Government was a deliberate attempt to restore political stability and order following the tumultuous years of the English Civil Wars and the execution of King Charles I. The new settlement sought to balance the necessity of a strong executive authority with the principles of parliamentary representation, although it ultimately entrenched significant military influence within the governance of the nation. As Lord Protector, Cromwell was granted the power to oversee administration and foreign policy, supported by a Council of State.

The establishment of the Protectorate marked a departure from the previous republican experiment, concentrating power in a manner that mirrored the authority once held by the monarchy. While the settlement aimed to provide a framework for a more settled government, it remained a contentious arrangement that reflected the deep divisions of the era. The key features of this transition included:

• The formal adoption of the Instrument of Government as the nation's written constitution.
• The consolidation of executive authority under the office of the Lord Protector.
• The creation of a Council of State to advise and assist in national governance.
• The continued reliance on the New Model Army to maintain domestic security.
• The attempt to provide a stable political structure following the collapse of the Rump Parliament.

Throughout his tenure, Cromwell faced the ongoing challenge of reconciling his role as a military leader with the requirements of civilian administration. The Protectorate represented a unique phase in Stuart Britain, characterised by an effort to institutionalise the gains of the parliamentary cause while navigating the complexities of ruling a fractured country. This period of rule would continue to shape the political landscape until the eventual restoration of the monarchy in 1660.