Definition
An act, omission, or conduct that violates the recognized privileges of a legislative body — whether a house of parliament, the U.S. Congress, or a state legislature — and is treated by that body as an offense against its dignity and authority. The offense may be committed by a member of the body (through misconduct, unauthorized disclosure, or breach of internal rules) or by an outsider (through obstruction, threats against members, or interference with legislative proceedings).
Because legislatures are the judges of their own privileges, a breach of privilege is not defined by a fixed statutory list. The offending house determines, when the question arises, whether a particular act constitutes a breach and what punishment, if any, to impose. The range of punishable conduct has historically included: bribery of members, assault on members for votes given, publication of proceedings without authorization, contemptuous language directed at the house or its members, and obstruction of the legislative process.
Common Confusion
BREACH OF PRIVILEGE vs. CONTEMPT OF PARLIAMENT/CONGRESS: The two concepts are closely related but not identical. Contempt of a legislative body is the broader category — any act that obstructs or disrespects the house in the exercise of its functions. Breach of privilege is narrower, referring specifically to interference with a recognized, established privilege. In practice, the terms are often used interchangeably in legislative proceedings, and the distinction matters more in British parliamentary practice than in American usage, where "contempt of Congress" dominates. Researchers should not assume that a historical source using one term is addressing precisely the same conduct as a source using the other.
Why It Matters in Research
The primary research trap is jurisdictional layering. The concept originates in British parliamentary law, where the privileges of Parliament are ancient, largely uncodified, and enforced by the houses themselves with considerable independence from the courts. American sources borrowed the framework but applied it within a constitutional structure that imposes limits — the Speech or Debate Clause (U.S. Const. art. I, § 6) provides constitutional grounding for congressional privilege, while state legislative privilege varies considerably by state constitution and statute.
Historical sources — including Rapalje & Lawrence and earlier editions of Black's — are written primarily with Parliament in mind and use parliamentary terminology and procedure. American researchers applying these definitions to Congress or state legislatures must adjust for structural differences: American courts have been more willing to review claims of legislative privilege than British courts, and the scope of recognized privileges differs.
The term also appears in different procedural contexts. In parliamentary sources, "breach of privilege" often triggers a formal complaint, a committee referral, and a house resolution — a distinct procedural track. In American legislative research, the same conduct may be addressed through contempt proceedings with different procedural rules. Researchers tracing a specific incident should identify which body and which procedural track applies before importing definitions across systems.
Finally, note that this term does not overlap with "breach of contract" or other private-law breach concepts. The encyclopedia entries flagged above address breach in commercial contexts and are not relevant to this term.
Historical Dictionary Support
Black's Law Dictionary offers a minimal definition — an act or default violating the privilege of either house of parliament, Congress, or a state legislature — that is accurate but descriptive only. It signals the scope of covered bodies without explaining the nature of privileges or the mechanism of enforcement.
Rapalje & Lawrence is more instructive. Their entry frames breach of privilege as a species of contempt of the High Court of Parliament, reflecting the historical understanding that Parliament's enforcement power derives from its character as a court. The parallel they draw — both houses punish by commitment or otherwise, as courts of law and equity do for contempt of court — is essential context. It explains why legislative bodies historically needed no external judicial authorization to punish offenders: the privilege enforcement power was understood as inherently judicial. This framing persists in British constitutional theory but sits uneasily in American separation-of-powers doctrine, where the judicial character of legislative privilege enforcement has been more contested.
Neither source addresses the limits that constitutional provisions place on American legislative privilege, the role of courts in reviewing privilege claims, or the distinction between individual-member privilege (Speech or Debate) and institutional house privilege. Researchers relying solely on these historical entries will have an incomplete picture for American practice.
Jurisdictional Note
In British parliamentary practice, breach of privilege remains largely self-regulated, with courts historically deferring to each house's determination of its own privileges. In the United States, constitutional provisions — particularly the Speech or Debate Clause — define and limit congressional privilege, and federal courts have adjudicated its scope. State legislative privilege varies significantly: some states have broad constitutional speech or debate protections; others offer narrower statutory or common-law protection.