Definition
A Member of Parliament (MP) is a person who holds a seat in a legislative body formally designated as a parliament. In its most precise legal sense, the term refers to an individual elected or, in some systems, appointed to serve as a representative in a national or subnational parliament, with the rights and privileges attendant to that office.
The term carries different meanings depending on the constitutional system in which it appears:
1. United Kingdom. In British constitutional law — the context from which Black's derives its definition — a Member of Parliament is a person entitled to sit and vote in either the House of Commons or the House of Lords. In modern usage, "MP" almost exclusively refers to elected members of the House of Commons. Members of the House of Lords hold their seats by peerage, appointment, or ecclesiastical office and are not typically styled "MPs" in contemporary practice, though historically the definition encompassed both houses.
2. Commonwealth and comparative systems. In Commonwealth countries (Canada, Australia, India, New Zealand, and others), the term designates elected representatives to the lower or primary legislative chamber. The precise entitlements of membership — including immunity from civil suit, freedom of speech within the chamber, and procedural rights — are governed by the constitutional instruments and standing orders of each parliament.
3. General comparative usage. In international and comparative legal writing, "member of parliament" is used generically to describe any legislator sitting in a body called a parliament, without implying the specific privileges of the Westminster model.
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Common Language
Modern common usage (Wiktionary): A representative elected by the voters of an electoral district to a house of a parliament.
Historical legal usage (Black's Law Dictionary): One having the right to sit in either house of the British parliament.
The common definition captures the electoral dimension accurately for most modern democracies. The legal gap is parliamentary privilege: being a member of parliament is not merely a political status but a legal one, carrying immunity from certain civil processes, freedom of speech within proceedings, and protections against interference that do not attach to ordinary citizens or even to other elected officials. The common definition omits this legal architecture entirely.
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Why It Matters in Research
Historical sources require care. Black's definition — "one having the right to sit in either house" — reflects a constitutional moment when the Lords and Commons were both active legislative chambers of roughly comparable legal standing. Researchers reading 19th-century materials should not assume that references to a "Member of Parliament" are limited to elected representatives. Hereditary peers, law lords, and bishops sitting in the Lords were all MPs in the legal sense of that era.
Parliamentary privilege is the primary legal dimension. When this term appears in legal disputes — typically involving defamation, contempt, or interference with a legislator's duties — the question is not simply whether someone holds a seat but whether the conduct in question falls within the protected scope of parliamentary proceedings. Research into parliamentary privilege requires tracing the Bill of Rights 1689 (Art. 9) in the British context, and the analogous constitutional provisions in Commonwealth jurisdictions.
The term is not a U.S. legal term. American legal materials will not use "Member of Parliament" to describe legislators. Researchers working on comparative constitutional law, international human rights instruments, or extradition and immigration matters (where the political status of foreign nationals may become relevant) will encounter the term in those cross-border contexts.
Immigration and refugee law. Foreign nationals claiming refugee status or asylum based on political persecution sometimes assert membership in a parliament or opposition party as evidence of targeted political status. In those proceedings, "member of parliament" functions as a factual status with legal consequence, not as a term of art in U.S. domestic law.
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Historical Dictionary Support
Black's Law Dictionary offers the minimum viable definition: "One having the right to sit in either house of the British parliament." This is technically accurate but does nothing to illuminate parliamentary privilege, the distinction between elected and non-elected members, or the evolution of membership as the Lords was progressively reformed (most notably by the House of Lords Act 1999, which removed most hereditary peers). The definition is a snapshot, not a guide.
Historical legal dictionaries generally treat this as a status term rather than a substantive legal concept, leaving the doctrine of parliamentary privilege to be treated separately. Researchers should expect that dictionaries define the status and that privilege is handled in constitutional law treatises and parliamentary manuals such as Erskine May.
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Jurisdictional Note
The legal content of "Member of Parliament" varies substantially by constitutional system. UK members enjoy privileges rooted in the Bill of Rights 1689. Canadian MPs derive their protections from the Constitution Act 1867 and the Parliament of Canada Act. Australian and Indian members operate under their own parliamentary statutes. Researchers should not transpose the privileges of one system onto another without verifying the applicable constitutional instrument.
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