In 1195, Richard I ("the Lionheart") of England and his Minister Hubert Walter commissioned certain knights to preserve the peace in unruly areas. They were responsible to the King for ensuring that the law was upheld and preserving the "King's peace". Therefore, they were known as "keepers of the peace".
An act of 1327 had referred to "good and lawful men" to be appointed in every county in the land to "guard the peace"; such individuals were first referred to as conservators of the peace, or wardens of the peace. The title justice of the peace derives from 1361, in the reign of Edward III. The "peace" to be guarded is the sovereign's, the maintenance of which is the duty of the Crown under the royal prerogative. Justices of the peace still use the power conferred or re-conferred on them since 1361 to bind over unruly persons "to be of good behaviour". The bind over is not a punishment, but a preventive measure, intended to ensure that people thought likely to offend will not do so. The justices' alternative title of "magistrate" dates from the 16th century, although the word had been in use centuries earlier to describe some legal officials of Roman times.
In the centuries from the Tudor period until the onset of the Industrial Revolution, the JPs constituted a major element of the English (later British) governmental system, which had been termed sometimes squirearchy (i.e., dominance of the land-owning gentry). For example, historian Tim Blanning notes that while in Britain the royal prerogative was decisively curbed by the Bill of Rights 1689, in practice the central government in London had a greater ability to get its policies implemented in the rural outlying regions than could contemporary absolute monarchies such as France – a paradox due especially to JPs belonging to the same social class as the Members of Parliament and thus having a direct interest in getting laws actually enforced and implemented on the ground.
Being an unpaid office, undertaken voluntarily and sometimes more for the sake of renown or to confirm the justice's standing within the community, the justice was typically a member of the gentry. The justices of the peace conducted arraignments in all criminal cases, and tried misdemeanours and infractions of local ordinances and bylaws. Towns and boroughs with enough burdensome judicial business that could not find volunteers for the unpaid role of justice of the peace had to petition the Crown for authority to hire a paid stipendiary magistrate.
The Municipal Corporations Act 1835 stripped the power to appoint normal JPs from those municipal corporations that had it. This was replaced by the present system, where the Lord Chancellor nominates candidates with local advice, for appointment by the Crown.