A Prime Minister is the most senior minister of cabinet in the executive branch of government in a parliamentary system. The position is usually held by, but need not always be held by, a politician. In many systems the Prime Minister selects and can dismiss other members of the cabinet, and allocates posts to members within the Government. In most systems, the prime minister is the presiding member and chairperson of the cabinet. In a minority of systems, notably in semi-presidential system of government, a prime minister is the official who is appointed to manage the civil service and execute the directives of the President.

In parliamentary systems fashioned after the Westminster system, the prime minister is the presiding and actual head of the government and head of the executive branch. In such systems, the head of state or the head of state's official representative (i.e the Monarch, President, or Governor-General), although officially the head of the executive branch, in fact holds a ceremonial position. The Prime Minister is often, but not always, a member of parliament and is expected with other ministers to ensure the passage of bills through the legislature. In some monarchies the monarch may also exercise executive powers (known as the Royal Prerogative) which are constitutionally vested in the Crown and can be exercised without the approval of parliament.

As well as being Head of Government, a prime minister may have other roles or titles — the Prime Minister of the United Kingdom, for example, is also First Lord of the Treasury and Minister for the Civil Service. Prime ministers may take other ministerial posts — for example during the Second World War Winston Churchill was also Minister of Defence (although there was then no Ministry of Defence). Former Australian prime minister Gough Whitlam was famous for forming his cabinet entirely of himself and his deputy as soon as the overall result was beyond doubt at the 1972 federal election (see First Whitlam Ministry).

History

While the modern office of Prime Minister was developed in the UKFact: date=August 2008 the first actual usage of the word Prime Minister or Premier Ministre was used by Cardinal Richelieu, when, in 1624 he was named to head the royal council as prime minister of France. Louis XIV and his descendants generally attempted to avoid giving this title to their chief ministers. The term Prime Minister in the sense that we know it originated in the 18th century in the United Kingdom.Fact: date=August 2008 Since medieval times Kings of England and the United Kingdom had ministers in whom they placed special trust and who were regarded as the head of the government. Examples were Thomas Cromwell under Henry VIII; William Cecil, Lord Burghley under Elizabeth I; Clarendon under Charles II and Godolphin under Queen Anne. These ministers held a variety of formal posts, but were commonly known as "the Minister," the "first Minister" and finally the "Prime Minister."