If someone lies under oath in court, they have committed perjury, a felony that carries up to five years in federal prison and comparable penalties in nearly every state.1Office of the Law Revision Counsel. 18 USC 1621 Perjury Generally What happens if someone lies in court goes well beyond a possible prison sentence, though. The liar can lose their case the moment the judge or jury stops believing them, see a judgment they already won set aside, be held in contempt on the spot, and carry a felony record that follows them into their job, their voting rights, and, if they aren’t a U.S. citizen, their immigration status.
When a Lie Legally Counts as Perjury
Not every false statement in a courtroom is perjury. Federal law requires four things, all at once. The speaker has to be under oath or signing something under penalty of perjury, which covers live testimony, depositions, affidavits, and written declarations submitted to a court or grand jury. The statement has to be false. The speaker has to have known it was false when they said it; honest mistakes and faulty memories do not qualify, no matter how wrong the statement turns out to be. And the lie has to be “material,” meaning it was capable of affecting the outcome of the proceeding. It doesn’t have to have actually changed the verdict.1Office of the Law Revision Counsel. 18 USC 1621 Perjury Generally
Lying about the speed of a car in a crash trial is material. Lying about a trivial detail with no bearing on any issue is not. The deliberate-knowledge requirement is why most perjury cases turn on proving what the witness knew, not just what they said.
How Lies Get Caught
The opposing attorney’s main tool is cross-examination. Skilled cross-examiners rarely extract dramatic confessions. They highlight inconsistencies between what the witness just said and what other evidence shows, pressing on details until the story holds or collapses under its own weight.
Attorneys can also formally impeach a witness. Under the Federal Rules of Evidence, any party may attack a witness’s credibility, including the party that called the witness in the first place.2Cornell Law School. Federal Rules of Evidence Rule 607 Impeachment often involves pulling out prior inconsistent statements, emails, or documents that directly contradict the testimony. Once the jury sees a text message that flatly disproves what a witness just said, the damage spreads past that single point and jurors start questioning everything else the witness told them.
Judges have their own tools. A judge who concludes testimony is false can strike it from the record and instruct the jury to disregard it. If false testimony has poisoned the proceeding badly enough that a fair outcome is no longer possible, the judge can declare a mistrial. In extreme cases, where a witness lies openly in front of the court, the judge can hold that person in contempt and impose immediate sanctions, including jail time.
Prison Time and Fines
A perjury charge is a separate criminal case, filed independently from whatever case the lie was told in. Under federal law, perjury is a felony punishable by up to five years in prison.1Office of the Law Revision Counsel. 18 USC 1621 Perjury Generally Federal fines for felony convictions can reach $250,000 for an individual.3Office of the Law Revision Counsel. 18 USC 3571 Sentence of Fine
A related federal statute specifically covers false declarations before a grand jury or court. It also carries up to five years in prison, climbing to ten years if the proceeding involves foreign intelligence surveillance.4Office of the Law Revision Counsel. 18 USC 1623 False Declarations Before Grand Jury or Court
State perjury laws vary, but nearly every state treats it as a felony. Prison terms typically run from roughly one to four years, with some states imposing longer sentences for lies told during serious felony trials. Judges tend to calibrate the sentence to the damage. Lying in a small civil dispute and lying in a murder trial are both perjury, and both get treated very differently at sentencing.
What It Does to the Case Itself
The most immediate fallout happens inside the case where the lie was told. Credibility in a courtroom is fragile. Once a judge or jury catches a witness in a lie, they tend to discount everything else that witness said. Jury instructions commonly tell jurors they are free to reject all of a witness’s testimony if they find the witness lied about any part of it.
That credibility collapse can be devastating. A personal injury plaintiff who exaggerates their injuries and gets caught may watch the jury decide the entire claim is fabricated and return a defense verdict. A criminal defendant whose key witness is proven to have lied loses that testimony entirely, and the jury often draws its own conclusions about why the witness felt the need to lie in the first place.
Perjury can also undo a case after it’s over. A party who discovers the other side won through false testimony can move to have the judgment set aside. Under Federal Rule of Civil Procedure 60(b)(3), a court can vacate a judgment obtained through fraud or misrepresentation, though the motion generally has to be filed within one year of the judgment. In severe cases involving what courts call “fraud upon the court,” there is no fixed time limit, but the bar for proving it is high. Judges can also order the party responsible for the false testimony to pay the other side’s attorney’s fees as a sanction.
Taking It Back Before It’s Too Late
Federal law gives a witness who lied a narrow window to recant. Someone who gave a false declaration in a court or grand jury proceeding can avoid prosecution by admitting the lie during the same continuous proceeding, but only if two conditions still hold: the false statement hasn’t already substantially affected the proceeding, and it hasn’t yet become obvious that the lie has been or will be exposed.4Office of the Law Revision Counsel. 18 USC 1623 False Declarations Before Grand Jury or Court
Both conditions have teeth. If prosecutors have already shifted strategy based on the false testimony, the first door is closed. If the opposing attorney has pulled up contradictory messages and is about to confront the witness with them, the second door is closed. The recantation defense rewards people who come clean on their own, not people who backpedal when cornered.
Pressuring Someone Else to Lie
Convincing someone else to lie under oath is its own federal crime: subornation of perjury. It carries the same punishment as perjury, up to five years in prison and fines up to $250,000.5Office of the Law Revision Counsel. 18 USC 1622 Subornation of Perjury The person doing the coaching faces the same maximum sentence as the person who delivers the lie on the stand.
When the conduct goes beyond pressuring a single witness into broader efforts to corrupt the process, federal obstruction of justice charges can apply. Obstruction carries up to ten years in prison in most cases and up to twenty years when tied to certain serious felony trials.6Office of the Law Revision Counsel. 18 USC 1503 Influencing or Injuring Officer or Juror Generally Prosecutors sometimes stack perjury, subornation, and obstruction charges against people involved in organized efforts to manipulate testimony.
Consequences That Outlast the Sentence
A perjury conviction is a felony, and felony convictions carry consequences that keep working long after the prison term ends. Depending on the state, a convicted felon may lose the right to vote, at least temporarily. Federal law disqualifies people convicted of crimes punishable by more than one year in prison from serving on a federal jury unless their civil rights have been restored. Many professional licensing boards treat a perjury conviction as disqualifying, especially in fields built on financial trust; the SEC, for example, can revoke or suspend the registration of an investment adviser convicted of perjury within the preceding ten years.
For non-citizens, the fallout can be worse than the sentence. The U.S. State Department classifies perjury as a crime involving moral turpitude, which can make a person ineligible for a visa or deportable if convicted. Limited waivers exist for immigrants who are close relatives of U.S. citizens or lawful permanent residents and can show extreme hardship, but no waiver is available if the conviction also involved murder or torture. Nonimmigrants can request a discretionary waiver, though approval requires a favorable recommendation and is not guaranteed.7U.S. Department of State. 9 FAM 302.3 Ineligibility Based on Criminal Activity
Lying to the Government Outside the Courtroom
Perjury law covers statements made under oath. A separate federal statute reaches lies told to the federal government even when no one was sworn in. Knowingly making a false statement to any branch of the federal government is itself a crime, punishable by up to five years in prison, or eight years when the false statement involves terrorism.8Office of the Law Revision Counsel. 18 USC 1001 Statements or Entries Generally That is the statute that catches people during FBI interviews, IRS audits, and federal agency investigations. People understand the stakes when they raise their right hand. They often don’t realize they’re in equivalent jeopardy during a conversation that feels casual.