The office of Lord-Lieutenant is of military origin and can be said to date from the reign of Henry VIII, when its holder was made responsible for the maintenance of order and for all military measures necessary locally for defence. By 1569, provision was made for the appointment of deputies. Although by the Regulation of the Forces Act 1871 the Militia was removed from the Lord-Lieutenant's direct control, it was not until 1921 that the Lord-Lieutenant finally lost the power to call on all able-bodied men of the County to fight in case of need.

The traditional links with the armed forces have been preserved in a modern form in the association of the Lord-Lieutenant with the volunteer Reserve Forces and through links with the local armed forces, police, fire and ambulance services. From the earliest days, the Lord-Lieutenant was closely associated with the magistracy. Until the Nineteenth century the Lord-Lieutenant was appointed the Clerk of Peace. In the English and Welsh shires, the Lord-Lieutenant is often a magistrate, chairman of the Advisory Committee and Keeper of the Rolls.