A prime minister, or premier, is the chief member of the cabinet in a parliamentary government and, as such, the head of government. A prime minister is not the head of state. In a republic, that position is held by the president; in a monarchy, by the sovereign.

The prime minister is normally chosen by the head of state from among elected members of the legislature; this choice is usually limited to the leader of the party in control of the legislature. The prime minister, who continues to serve in the legislature, selects a cabinet, formulates and administers government policy, and dispenses party patronage. Prime ministers are generally chosen for an indefinite term, and in democratic countries the support of the legislative body is required. Should this support be withdrawn, the resignation of the prime minister and the cabinet is in order. The prime minister has the right to call for the resignation of a cabinet member at any time, and cabinet members who oppose government policy are expected to resign.

In Great Britain the prime minister may call for a general election by asking the sovereign to dissolve Parliament and is required to do so if ruling policies have met with decisive defeat in the House of Commons. The prime minister there is by modern convention a member of the House of Commons, although it was formerly the practice to select prime ministers from the House of Lords as well.

Historically, the office of prime minister developed from the growing power of Parliament in the 17th and 18th centuries. The monarchs, who had previously depended on their own courtiers for political advice, found it advantageous to have a supporter in Parliament, especially to aid the monarch in levying taxes. Robert Walpole is generally regarded as the first prime minister. The power of the office grew during the 19th century, as the power of the crown declined.

Bibliography: Blake, Lord, The Office of Prime Minister (1975); Englefield, Dermot, Facts about British Prime Ministers: A Compilation of Biographical and Historical Information (1995); Hennessy, Peter, The Prime Minister: The Office and Its Holder since 1945 (2001); Jennings, Sir William I., Cabinet Government, 3d ed. (1979); Rose, Richard, and Suleiman, E. N., Presidents and Prime Ministers (1980); Thomas, Graham P., Prime Minister and Cabinet Today (1998).