The office of Lord-Lieutenant is military in 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. A full account of the history of Lord-Lieutenants is given in Miles Jebb's The Lord-Lieutenants and their Deputies (History Press, 2007).

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. Lord-Lieutenants' connections with uniformed organisations have led to links with other uniformed organisations, such as police, fire and ambulance services and many voluntary bodies, such as Red Cross, the cadet forces and other national and local youth organisations. In recent years the circles within which the Lord-Lieutenant's leadership role is exercised have come to include a wide range of matters, civil and defence, professional and voluntary. Lord-Lieutenant's are effective in such work largely because of their links to the Crown and the essentially voluntary and apolitical nature of their role.

From earliest days the Lord-Lieutenant was closely associated with the magistracy. Until the 19th century the Lord-Lieutenant appointed the Clerk of the Peace. In England the Lord-Lieutenant is still usually the Chairman of the Advisory Committee which appoints magistrates.

The office of Lord-Lieutenant has been provided for in statute, most recently by the Lieutenancies Act 1997. The Queen appoints Lord-Lieutenants on the recommendation of the Prime Minister, and approves the appointment of Vice Lord-Lieutenants.The Queen may also disapprove of the proposed appointment of a Deputy Lieutenant.

The Lord-Lieutenant's role is essentially non-political. She is required at all times to exercise tact and sometimes forbearance in order to avoid being involved in controversy, which might lead to the impartiality of her attitude being questioned. As The Queen's representative, she stands aloof from politics in her county and does not take part in political activities in her area or hold office in local political party organisations. Her spouse also takes the same stance.