Parliamentary supremacy, also known as Parliamentary sovereignty, is a principle in some countries with British parliamentary-style democracies, according to which sovereignty rests with the legislative assembly, rather than with the executive or judicial branches of government. The United Kingdom is the most prominent example of a national government in which parliamentary supremacy exists.
The basic principle of parliamentary supremacy states that any legislation passed by the parliamentary assembly is, by virtue of that fact, the highest law of the land, and cannot be set aside by any other branch of government, including the king or queen (if the country is a monarchy), the executive branch (the president or prime minister and his or her cabinet), or even the judiciary (the court system). This means that court judges may not overturn legislation, which often happens in constitutional democracies and representative republics with the rule of law, like the United States. It also means that only the Parliament has the power to repeal or amend legislation passed by a previous Parliament.
The oldest and most influential model of a government with Parliamentary supremacy is the government of the United Kingdom. As the British Parliament explains, the U.K. has an “unwritten constitution” – that is, there is no single document setting out the powers and responsibilities of the government, as there now is the U.S., Canada, and many other countries. Instead, the UK’s “constitution” consists of an informal collection of legislation passed by Parliament, conventions (traditions that have been followed for so long that they have the force of law), and “royal prerogatives,” or powers which have been reserved to the reigning King or Queen (and of which there are now very few). In general, Parliament alone holds the power to call the Prime Minister and Cabinet to account, pass legislation to the Crown for royal assent, and set aside or amend already existing laws.
Although this may seem like a situation ripe for the abuse of power, historically, the doctrine of Parliamentary sovereignty was actually established in order to limit government power – specifically, the power of the Crown and the executive. While revolutionary America sought to restrict the power of the executive through a written constitution, the British more gradually developed the principle that while the reigning King or Queen could continue to rule the country officially, in practice, the Crown was stripped of all effective power to actually make political decisions. The power to implement and enforce laws was given to the Prime Minister and the Cabinet, and the power to make and unmake laws to Parliament. Furthermore, by convention, the Prime Minister must be a member of the House of Commons and all Cabinet ministers must be members of one of the houses of Parliament.
Some parliamentary countries with written constitutions, like Australia or Canada, are sometimes said to have parliamentary supremacy, because the executive branch (the Prime Minister and Cabinet) is accountable to Parliament. However, as the University of Alberta’s Centre for Constitutional Studies explains, there is an important distinction between parliamentary supremacy and constitutional democracy: “in a constitutional democracy, Parliament is not omnipotent. Its powers are constrained by the Constitution.” The Parliament may have the power to issue instructions to the executive branch, but any legislation it passes is still subject to the Constitution, as interpreted by the judiciary (the courts).