Definition
A mistrial is a trial that is terminated before a valid verdict is reached and given no legal effect. The proceeding is treated as though it never concluded, and — depending on the cause — the case may be retried without violating double jeopardy protections.
Two distinct situations produce a mistrial:
1. Procedural or jurisdictional defect. The trial was fundamentally flawed from the start or became so during proceedings — through lack of jurisdiction, an improperly drawn jury, the absence of a proper issue (e.g., no plea entered), or some other failure of a foundational requisite. The proceeding is void or nugatory, not merely irregular.
2. Jury discharge without verdict. The jury is dismissed before reaching a verdict — most commonly because the jury is deadlocked (a hung jury) but also because of juror misconduct, juror incapacity, prejudicial publicity, or other circumstances making continuation impossible or unjust. This is the dominant modern usage.
Common Language
Modern common usage (Wiktionary): A trial prematurely ended upon being declared invalid because of an error in procedure, or because of a hung jury.
Historical common usage (Webster's 1913): A false or erroneous trial; a trial which has no result.
The common definitions are serviceable but compress two legally distinct situations into one. In practice, the procedural-defect mistrial and the hung-jury mistrial carry different double jeopardy consequences and are governed by different doctrines. Researchers who treat "no result" as a single category will miss this distinction.
Common Confusion
MISTRIAL vs. HUNG JURY: A hung jury is one cause of a mistrial — not a synonym for it. A mistrial can occur before jury deliberations ever begin. Conversely, a hung jury always produces a mistrial, but the reverse is not true. Historical sources sometimes use "mistrial" to describe what modern courts would call a hung-jury mistrial specifically, which can mislead researchers reading older opinions.
MISTRIAL vs. REVERSAL ON APPEAL: A mistrial terminates a trial in progress. A reversal on appeal nullifies a completed verdict after judgment. The two are procedurally and constitutionally distinct, though both may result in a new trial.
Core Elements
For a valid declaration of mistrial (jury-discharge type), courts generally require:
— Manifest necessity or the defendant's consent. The constitutional standard for retrial without double jeopardy violation turns on whether manifest necessity existed to discharge the jury. Absent manifest necessity or defendant's consent to discharge, a second trial is barred.
— Judicial declaration. A mistrial requires an affirmative court declaration; a jury simply failing to report is not itself a mistrial.
— No final verdict. Once a verdict is returned and accepted, the proceeding cannot be recharacterized as a mistrial.
Why It Matters in Research
The term carries two operational meanings that coexisted in historical sources but have diverged in modern doctrine. Pre-twentieth-century opinions and treatises often use "mistrial" primarily for the procedural-defect sense — a void or erroneous trial — while contemporary courts use it almost exclusively for jury discharge. A researcher reading an 1890 opinion declaring a "mistrial" should not assume it involved a hung jury.
The double jeopardy dimension is the most consequential modern issue and is almost entirely absent from the historical dictionaries. Whether a defendant may be retried after a mistrial depends on the cause: mistrials declared with manifest necessity do not bar retrial; mistrials caused by prosecutorial overreach or declared without necessity may. This constitutional overlay developed through case law and is not reflected in the dictionary definitions at all.
Jurisdictional variation in what constitutes "manifest necessity" makes corpus research sensitive to the court and era. Federal circuit treatment and state supreme court doctrine can diverge significantly on specific triggering circumstances (juror illness, juror misconduct discovered mid-trial, etc.).
Researchers should also note that mistrial motions in civil cases follow different standards than in criminal cases, and historical sources do not always distinguish between them. Bouvier's definition, which references a civil-era federal report alongside common law criminal examples, illustrates this blending.
Historical Dictionary Support
The historical sources agree on the core: a mistrial is an erroneous, invalid, or nugatory trial — one that cannot stand in law. Black's (both editions) and Burrill share nearly identical language tracing to the defect-based concept: wrong county, wrong jury draw, want of jurisdiction. Bouvier adds the more modern usage explicitly, noting that where a jury is discharged without a verdict "the proceeding is properly known as a mistrial," citing an 1885 federal report — an early acknowledgment of the hung-jury application in American law.
Rapalje & Lawrence reduces the entry to "an erroneous trial" with no elaboration, and Anderson's Dictionary of Law declines to define it independently at all, directing readers to TRIAL. Neither source adds analytical value.
None of the historical dictionaries address double jeopardy consequences, constitutional standards for discharge, or the manifest necessity doctrine — the doctrinal substance that makes mistrial practically significant in modern criminal research. Researchers should treat the historical definitions as identifying the concept only, not as guidance on its legal consequences.
Jurisdictional Note
The manifest necessity standard for retrial after mistrial is a federal constitutional floor, but states apply it with varying stringency and define triggering circumstances differently. In civil proceedings, mistrial standards are governed by procedural rules that vary by jurisdiction and have no double jeopardy dimension.
Encyclopedia Cross-Reference
Mistrial and Hung Jury — The Law Mind Criminal Law Encyclopedia (criminal_212)