Montana Manslaughter Laws: Mitigated and Negligent Homicide (2026)

Montana has no crime called manslaughter. The offenses that cover the same ground are mitigated deliberate homicide (MCA 45-5-103), a purposeful or knowing killing committed "under the influence of extreme mental or emotional stress for which there is reasonable explanation or excuse," punishable by 2 to 40 years, and negligent homicide (45-5-104), negligently causing a death, punishable by up to 20 years. Deaths caused by impaired driving are vehicular homicide while under the influence (45-5-106, up to 30 years) and, since October 1, 2025, aggravated vehicular homicide while under the influence (45-5-107, 3 to 30 years).

For other states, see our guide to manslaughter laws by state.

Information last verified on 2026-10-18. This article has not been reviewed by a licensed lawyer.

Jurisdiction scope: This article covers the Montana statutes on homicide below deliberate homicide: mitigated deliberate homicide (MCA 45-5-103), negligent homicide (45-5-104), vehicular homicide while under the influence (45-5-106), aggravated vehicular homicide while under the influence (45-5-107), and the related sentencing, licence and traffic statutes. It does not cover deliberate homicide sentencing (see how long a life sentence is in Montana and our overview of murder sentencing guidelines), self-defense (see Montana self-defense laws), civil lawsuits by surviving family (see Montana wrongful death law), or federal offenses, which the manslaughter laws hub covers.

What is manslaughter in Montana?

Part 1 of Title 45, chapter 5 ("Homicide") contains no section named manslaughter. Montana's equivalent of murder is deliberate homicide (45-5-102), and the offenses below it are graded by mental state:

• Mitigated deliberate homicide (45-5-103) covers what other states call voluntary manslaughter. It is still a purposeful or knowing killing; the mitigation is extreme mental or emotional stress.
• Negligent homicide (45-5-104) covers what other states call involuntary manslaughter.
• Vehicular homicide while under the influence (45-5-106) and aggravated vehicular homicide while under the influence (45-5-107) cover deaths caused by impaired driving.

Montana's Criminal Code recognises three mental states, purposely, knowingly and negligently, and every offense other than felony murder and absolute-liability offenses requires one of them for each element (45-2-103(1)). Recklessness is not one of those general mental states, and none of the homicide offenses in Part 1 is built on it.

Is manslaughter a felony in Montana?

Yes. Montana defines a felony as "an offense in which the sentence imposed upon conviction is death or imprisonment in a state prison for a term exceeding 1 year" (45-2-101). Each offense below carries a possible state prison term far longer than a year.

Montana does not sort felonies into classes; each offense statute sets its own range. For an overview of how Montana grades crimes, see Montana felony and misdemeanor classes.

Mitigated deliberate homicide (Montana's voluntary manslaughter)

"(1) A person commits the offense of mitigated deliberate homicide when the person purposely or knowingly causes the death of another human being or purposely or knowingly causes the death of a fetus of another with knowledge that the woman is pregnant but does so under the influence of extreme mental or emotional stress for which there is reasonable explanation or excuse. The reasonableness of the explanation or excuse must be determined from the viewpoint of a reasonable person in the actor's situation." MCA 45-5-103(1)

Montana's test is extreme mental or emotional stress, not "heat of passion" or "sudden quarrel." The statute is a reduction from deliberate homicide, and three features of its text matter:

• The burden of proof. "Mitigating circumstances that reduce deliberate homicide to mitigated deliberate homicide are not an element of the reduced crime that the state is required to prove or an affirmative defense that the defendant is required to prove. Neither party has the burden of proof as to mitigating circumstances, but either party may present evidence of mitigation" (45-5-103(3)).
• Which deliberate homicide it reduces. It is a lesser included offense of deliberate homicide under 45-5-102(1)(a), the purposeful or knowing killing, but "is not a lesser included offense of deliberate homicide as defined in 45-5-102 (1)(b)," the felony-murder form (45-5-103(2)).
• The penalty. "A person convicted of mitigated deliberate homicide shall be imprisoned in the state prison for a term of not less than 2 years or more than 40 years and may be fined not more than $50,000, except as provided in 46-18-219 and 46-18-222" (45-5-103(4)).

In State v. Sanchez, 2008 MT 27, the Montana Supreme Court held that the jury instruction "accurately conveyed § 45-5-103, MCA, which unambiguously states that 'reasonable' modifies the explanation for the extreme mental or emotional stress, not the defendant's act of causing the death of another human being." Sanchez was convicted of deliberate homicide and the conviction was affirmed; the opinion predates the 2013 amendment that added the burden-of-proof language in subsection (3).

Panic defense. Section 45-5-103 contains no provision on a victim's sexual orientation or gender identity.

Self-defense and justification are separate questions; see Montana self-defense laws.

Negligent homicide (Montana's involuntary manslaughter)

"(1) A person commits the offense of negligent homicide if the person negligently causes the death of another human being. (2) Negligent homicide is not an included offense of deliberate homicide as defined in 45-5-102 (1)(b). (3) A person convicted of negligent homicide shall be imprisoned in the state prison for any term not to exceed 20 years or be fined an amount not to exceed $50,000, or both." MCA 45-5-104

The key word is negligently, and Montana's definition sets a high bar:

"'Negligently'--a person acts negligently with respect to a result or to a circumstance described by a statute defining an offense when the person consciously disregards a risk that the result will occur or that the circumstance exists or when the person disregards a risk of which the person should be aware that the result will occur or that the circumstance exists. The risk must be of a nature and degree that to disregard it involves a gross deviation from the standard of conduct that a reasonable person would observe in the actor's situation. 'Gross deviation' means a deviation that is considerably greater than lack of ordinary care." MCA 45-2-101

The definition reaches both a person who consciously disregards the risk and a person who should have been aware of it, as long as the disregard is a gross deviation. Negligent homicide has no minimum term, and section 45-5-104 does not bar a suspended or deferred sentence.

Negligent homicide is also the offense for a fatal crash by a driver who was not impaired, because both vehicular homicide offenses require a violation of the DUI statute. When negligent homicide results from the operation of a motor vehicle, the department must revoke the driver's licence for one year (61-5-205(1)(a), (3)).

Vehicular homicide and DUI deaths in Montana

Montana does not use the terms vehicular manslaughter or DUI manslaughter. It has two impaired-driving homicide offenses.

Vehicular homicide while under the influence

"(1) A person commits the offense of vehicular homicide while under the influence if the person negligently causes the death of another human being while the person is operating a vehicle in violation of 61-8-1002. ... (3) A person convicted of vehicular homicide while under the influence shall be imprisoned in a state prison for a term not to exceed 30 years or be fined an amount not to exceed $50,000, or both. Imposition of a sentence may not be deferred. (4) If the victim has a surviving minor child, a person convicted of vehicular homicide while under the influence must be ordered to pay restitution pursuant to 46-18-240." MCA 45-5-106

The DUI statute it refers to, 61-8-1002(1), makes it an offense to drive or be in actual physical control of a vehicle on the ways of the state open to the public "while under the influence of alcohol, any drug, or a combination of alcohol and any drug," or of a noncommercial vehicle with an alcohol concentration of 0.08 or more, among other forms. The child-support restitution rule in subsection (4) was added by 2025 HB 712 (Ch. 509), which has no effective-date section and so took effect October 1, 2025 under MCA 1-2-201; it did not change the offense's elements or its 30-year maximum.

Aggravated vehicular homicide while under the influence (2025)

"(1) A person commits the offense of aggravated vehicular homicide while under the influence if the person causes the death of another human being while the person is operating a vehicle in violation of 61-8-1002 (1)(a), (1)(b), (1)(c), or (1)(d) and in violation of aggravated driving under the influence as defined in 61-8-1001. ... (3) A person convicted of aggravated vehicular homicide while under the influence shall be imprisoned in a state prison for a term of not less than 3 years or more than 30 years or be fined an amount of at least $10,000 not to exceed $50,000, or both. Imposition of a sentence may not be deferred. The court may not suspend execution of the first 3 years of a sentence of imprisonment imposed under this subsection except as provided in 46-18-222 (1) through (5)." MCA 45-5-107

Aggravated driving under the influence means a DUI violation plus one of four conditions in 61-8-1001: an alcohol concentration of 0.16 or more; being under a court or department order to use an ignition interlock device; driving while the licence is suspended, cancelled or revoked because of a prior DUI violation; or refusing a breath test while the licence was suspended, cancelled or revoked under an implied consent statute.

The offense was created by 2025 HB 267 (Ch. 226, Laws of 2025). The act has no effective-date section, so under MCA 1-2-201(1)(a) it took effect "on the first day of October following its passage and approval," October 1, 2025. A death caused before that date falls under 45-5-106 or the other homicide statutes, not 45-5-107.

The 3-year rule is subject to 46-18-222, which lifts mandatory minimums and no-suspension rules where, among other listed situations, "the offender was less than 18 years of age at the time of the commission of the offense" or the offender's "mental capacity, at the time of the commission of the offense ... was significantly impaired."

Leaving the scene, fleeing police, reckless driving and racing

• Leaving the scene: a driver who knows or reasonably should have known of an accident with another person or a deceased person must stop and remain at the scene until the duties of 61-7-105 are met (61-7-103). Failing to comply "in an accident resulting in serious bodily injury ... or death of any person or resulting in the driver striking the body of a deceased person" is punishable by 1 to 10 years in state prison, a fine of up to $50,000, or both (61-7-118(3)), and a felony conviction under 61-7-103 brings a 2-year licence revocation (61-5-205(3)). See Montana hit-and-run laws.
• Fleeing a peace officer: "A person convicted of an offense of fleeing from or eluding a peace officer during which the person causes serious bodily injury to or the death of any other person is guilty of a felony and shall be imprisoned for a term not to exceed 10 years or fined an amount not to exceed $10,000, or both" (61-8-707(3)). That penalty section was created by 2025 HB 503 (Ch. 311), which reorganized the fleeing statutes. A fleeing conviction also triggers a 1-year licence revocation (61-5-205(1)(e), (3)).
• Reckless driving: a reckless driving conviction under 61-8-301 "whose offense results in the death or serious bodily injury of another person" is punishable by a fine of up to $10,000, up to 1 year of incarceration, or both (61-8-715(2)). The same penalty applies to reckless endangerment of emergency personnel or highway workers under 61-8-389, an offense created in 2023 (Ch. 567, L. 2023) that covers passing a stationary emergency or highway-worker vehicle in violation of 61-8-388 and endangering persons or property in a highway work zone.
• Speed contests: a 61-8-308 speed contest is a misdemeanor punishable by a fine of $50 to $500, up to 6 months in jail, or both (61-8-717); the section has no separate grade for a death.

Driving while a licence is suspended or revoked carries up to 6 months of imprisonment, a fine, or both (61-5-212), and that section has no separate grade for a resulting death; a suspension or revocation for a prior DUI is instead one of the aggravated-DUI conditions for 45-5-107. The boating-operation section that bars reckless, negligent or impaired operation of a motorboat or vessel (23-2-523) also has no grade for a resulting death.

Two related offenses do not require a death. Negligent vehicular assault (45-5-205) carries up to 10 years, a fine of up to $10,000, or both when the offender caused serious bodily injury. Criminal endangerment (45-5-207) carries up to 10 years, a fine of up to $50,000, or both. For DUI penalties when no one is hurt, see Montana DUI laws.

Unborn victims

Montana's fetal-death offenses are intentional ones. Deliberate homicide includes purposely or knowingly causing "the death of a fetus of another with knowledge that the woman is pregnant" (45-5-102(1)(c)), and mitigated deliberate homicide covers the same act under extreme mental or emotional stress (45-5-103(1)).

Negligent homicide and both vehicular homicide offenses apply to the death of "another human being," and Montana's Criminal Code defines a human being as "a person who has been born and is alive" (45-2-101).

Other offenses graded by a resulting death

• Distribution of a dangerous drug resulting in death: 45-9-101(5); "If the offense charged results in the death of an individual from the use of any dangerous drug that was distributed," up to 100 years in state prison and a fine of up to $100,000. It is a sentencing provision of the drug-distribution statute, not a homicide offense.
• Intentional vandalism to railroad property resulting in death: 69-14-1205(3)(d); up to 40 years in state prison, a fine of up to $50,000, or both.
• Reckless endangerment of emergency personnel or highway workers resulting in death: 61-8-389, 61-8-715(2); up to 1 year, a fine of up to $10,000, or both.

Montana's aiding or soliciting suicide offense (45-5-105) applies only where "such suicide does not occur," and carries up to 10 years, a fine of up to $50,000, or both.

Sentencing rules that apply

Weapon add-on. A person found guilty of an offense, other than one in which use of a weapon is an element, who "knowingly displayed, brandished, or otherwise used a firearm, destructive device ... or other dangerous weapon" while committing it must receive an additional 2 to 10 years in state prison, except as provided in 46-18-222 (46-18-221(1)). A second or later weapon offense adds 4 to 20 years (46-18-221(2)). The added term "must run consecutively to the sentence provided for the offense" (46-18-221(4)).

Persistent felony offenders. A persistent felony offender who was 21 or older at the time of the present offense faces 5 to 100 years in state prison, a fine of up to $50,000, or both (46-18-502(1)). The range is 10 to 100 years if, among other conditions, less than 5 years separate the present offense from the previous felony conviction or the release from it (46-18-502(2)). Except as provided in 46-18-222, the first 5 years of a 46-18-502(1) sentence, or the first 10 years of a 46-18-502(2) sentence, may not be deferred or suspended, and a 46-18-502(2) sentence must run consecutively to any other sentence (46-18-502(3)-(4)).

Repeat violent offenses. Mitigated deliberate homicide is listed in 46-18-219(1)(b): an offender convicted of it who was previously convicted of two offenses on that statute's lists (or comparable out-of-state or federal offenses) must be sentenced to life in prison, unless the death penalty is applicable and imposed. Except as 46-23-210 and 46-18-219(3) provide, an offender sentenced under it must serve the entire sentence in prison, may not be paroled and may not be given time off for good behavior (46-18-219(2)). Negligent homicide and the two vehicular homicide offenses are not on that list.

Parole. A prisoner serving a time sentence "may not be paroled under this section until the prisoner has served at least one-fourth of the prisoner's full term" (46-23-201(3)).

Violent-offender registration. Mitigated deliberate homicide is a "violent offense" under the Sexual or Violent Offender Registration Act (46-23-502(14)(a)(ii)). Negligent homicide and the vehicular homicide offenses are not on that list.

Recent changes

All three 2025 acts below lack an effective-date section, so each took effect October 1, 2025 under MCA 1-2-201:

• HB 267 (Ch. 226): created aggravated vehicular homicide while under the influence, 45-5-107.
• HB 712 (Ch. 509): added 45-5-106(4), mandatory restitution for the support of a victim's surviving minor child.
• HB 503 (Ch. 311): reorganized the fleeing and eluding statutes and placed the serious-injury-or-death penalty in 61-8-707(3).

The core homicide sections are older: 45-5-103 was last amended in 2013 and 45-5-104 in 1999.

Federal law, 18 U.S.C. 1112, separately covers manslaughter on federal land and in other federal jurisdictions; the manslaughter laws hub explains it.

Related pages

• Manslaughter laws by state
• Montana felony and misdemeanor classes
• Montana DUI laws
• Montana hit-and-run laws
• The difference between murder, homicide and manslaughter
• Wyoming manslaughter laws
• Idaho manslaughter laws

This article provides general legal information about Montana law as of 2026-10-18. It is not legal advice. For a specific situation, contact a lawyer licensed in Montana.

Last updated: 2026-10-18.

Frequently Asked Questions

Does Montana have manslaughter?

Not by that name. Montana's Criminal Code uses mitigated deliberate homicide (45-5-103) for a killing under extreme mental or emotional stress and negligent homicide (45-5-104) for a negligently caused death. Impaired-driving deaths are vehicular homicide while under the influence (45-5-106) or aggravated vehicular homicide while under the influence (45-5-107).

What is the sentence for mitigated deliberate homicide in Montana?

2 to 40 years in state prison, and a fine of up to $50,000 may be added, except as provided in 46-18-219 and 46-18-222 (45-5-103(4)).

What is the sentence for negligent homicide in Montana?

Up to 20 years in state prison, a fine of up to $50,000, or both (45-5-104(3)). There is no minimum term. If the death resulted from operating a motor vehicle, the licence is revoked for one year (61-5-205).

What is the difference between mitigated deliberate homicide and negligent homicide?

Mitigated deliberate homicide is a purposeful or knowing killing reduced by extreme mental or emotional stress with a reasonable explanation or excuse (45-5-103). Negligent homicide is an unintended death caused by a gross deviation from the standard of conduct of a reasonable person (45-5-104; 45-2-101).

What is the penalty for a DUI death in Montana?

Vehicular homicide while under the influence carries up to 30 years, a fine of up to $50,000, or both, with no deferred sentence (45-5-106). If an aggravated-DUI condition applies, such as a 0.16 alcohol concentration, aggravated vehicular homicide while under the influence carries 3 to 30 years or a fine of $10,000 to $50,000, or both, and the first 3 years of a prison sentence generally cannot be suspended (45-5-107, in effect October 1, 2025).

What happens if a sober driver causes a fatal crash in Montana?

Both vehicular homicide offenses require a DUI violation, so a non-impaired driver's fatal crash falls under negligent homicide (45-5-104) only if the driving meets Montana's gross-deviation definition of negligently. A reckless driving conviction whose offense results in a death carries up to 1 year, a fine of up to $10,000, or both (61-8-715(2)).

Is leaving the scene of a fatal crash a felony in Montana?

Failing to stop, remain, give information or render aid after an accident resulting in death or serious bodily injury carries 1 to 10 years in state prison, a fine of up to $50,000, or both (61-7-118(3)), plus a 2-year licence revocation on a felony conviction under 61-7-103 (61-5-205(3)).