Parliamentary sovereignty, also called parliamentary supremacy or legislative supremacy, is a concept in the constitutional law of some parliamentary democracies. It holds that the legislative body has absolute sovereignty and is supreme over all other government institutions, including executive or judicial bodies. It also holds that the legislative body may change or repeal any previous legislation and so it is not bound by written law (in some cases, not even a constitution) or by precedent. Changes to the constitution typically require a supermajority, often two thirds of votes instead of one half.

In some countries, parliamentary sovereignty may be contrasted with separation of powers and constitutionalism, which limits the legislature's scope often to general law-making and makes it subject to external judicial review, where laws passed by the legislature may be declared invalid in certain circumstances.

States that have sovereign legislatures include: the United Kingdom, New Zealand, the Netherlands, Sweden, Finland, Jamaica, Israel.

Under the federal system, neither the states nor the federal parliament in Australia have true parliamentary sovereignty. The Commonwealth Parliament is created by the federal constitution, and only has enumerated powers. Each state's legislative power is inherent but restrained by the federal constitution, the relevant state constitution, and Commonwealth powers. Nevertheless, in the Australian context, "parliamentary supremacy" is used contextually as a term and has two meanings: one is that parliament (the legislature) can make and unmake any law; another meaning is that as long as a parliament (legislature) has the power to make laws regarding a subject matter, the exercise of that power cannot be challenged or reviewed by the judiciary. The second meaning is more consistent with the federal system and the practice of judicial review, as the judiciary cannot review on the merits of the parliament (legislature)'s exercise of power.

Blackshield & Williams (2010) explain that "[i]n Australia, the idea of Parliamentary Sovereignty must be understood in the context of the rigid limits and boundaries imposed by the federal Constitution, and to some extent by the State Constitutions as well." Goss (2021) goes further and argues that the ideas of parliamentary sovereignty and parliamentary supremacy are "inaccurate, inadequate, or unnecessary" usages in Australian law.

The constitution confers the power to make laws in the Commonwealth Parliament, however, this is limited to particular subjects. Section 128 of the federal constitution prescribes the mode to alter the constitution, which further restricts the power of the Commonwealth Parliament.

The supremacy clause (section 109 of the constitution) gives Commonwealth laws precedence over state laws. The state law-making power is therefore constrained where the Commonwealth has concurrent law-making power. Furthermore, regarding the subject matters which Commonwealth has concurrent legislative power, the Commonwealth Parliament can "cover the field", which means the Commonwealth can, by express words or by implication, exclude the operations of state laws. The Commonwealth Parliament has exclusive legislative power over the subject matters listed in sections 52 and 92 of the constitution, which means that the states cannot make laws in these areas. Also, under section 96 of the constitution, the Commonwealth can use financial assistance to entice states to refrain from exercising their legislative powers, such as refraining from collecting income tax.

Each state parliament power is subject to procedural limitation, which is the entrenchment of restrictive legislative procedure. Section 6 of the Australia Act states that laws concerning the "constitution, power or procedure of the parliament" are invalid unless passed in the manner and form prescribed by the legislation made by the parliament.