Mental Illness Defence in Australian Criminal Law

The mental illness defence allows individuals to be found not criminally responsible If, at the time of the offence, they were suffering from a mental condition that prevented them from understanding their actions or knowing that what they were doing was wrong. This article will explore the legal definition of mental illness, the criteria courts use to assess criminal responsibility, relevant procedural steps, limitations of the defence, and the post-verdict consequences, such as detention in mental health facilities rather than prison. With extensive experience in complex criminal matters, Faraj Defence Lawyers provide expert representation in cases involving mental illness, ensuring your rights are protected and your circumstances fully understood by the court.

What is the Mental Illness Defence?

The mental illness defence; also known as the insanity defence or defence of mental impairment, is a legal principle in Australian criminal law that applies when a person is not criminally responsible for their actions due to a serious mental condition. This defence is based on the idea that an accused may be incapable of understanding the nature and quality of their actions, or incapable of knowing that their actions were wrong, at the time of the offence.

To succeed, the mental impairment must be diagnosed and medically supported, and it must be shown to have existed at the time of the alleged offence.

Importantly, this defence does not excuse criminal behaviour; rather, it recognises that a person suffering from a significant mental illness may lack the capacity to be held legally responsible.

Legal Criteria for Establishing the Defence

Key Elements of the Mental Illness Defence

To successfully establish the mental illness defence in Australian criminal law, certain legal requirements must be met. Courts rely on both medical evidence and legal tests to determine whether a person should be found not criminally responsible due to a mental impairment.

• Diagnosed Mental Condition at the Time of the Offence The accused must have been suffering from a recognised mental illness or cognitive impairment at the time the offence occurred. This typically includes conditions such as schizophrenia, psychosis, bipolar disorder, or severe intellectual disability. Diagnosis by a qualified psychiatrist or psychosis, bipolar disorder, or severe intellectual disability. Diagnosis by a qualified psychiatrist or psychologist is essential.

• Inability to Understand the Nature or Wrongfulness of the Act: The defence requires proof that, because of the mental illness, the accused either:

  • Did not understand the nature and quality of their actions, or

  • Did not know that their conduct was wrong.

Courts assess this based on psychiatric reports, witness testimony, and the accused’s behaviour before, during, and after the offence. The legal test is objective but informed by expert opinion.

The Role of Psychiatric Assessments

Psychiatric assessments are critical in cases involving the mental illness defence. They provide the medical foundation for determining whether an accused person was suffering from a mental impairment at the time of the offence and whether the impairment affected their ability to understand their actions or know they were wrong.

Mental health professionals, usually forensic psychiatrists or clinical psychologists; conduct in-dept evaluations, reviewing medical history, interviews, behavioural patterns, and the circumstances of the offence. They prepare formal reports and often give expert testimony in court, offering an opinion on the accused’s mental state during the alleged offence.

While courts are not bound by psychiatric findings, judges and juries give significant weight to expert medical evidence when deciding whether the legal threshold for the mental illness defence has been met. Conflicting reports may require cross-examination of experts.

Procedural Aspects of the Mental Illness Defence

Raising the Defence in Court

The mental illness defence can be raised at any stage of criminal proceedings, but it is most commonly introduced before or during trial, once sufficient evidence supports the claim. Either the defence or prosecution may raise the issue if there is reason to believe the accused was mentally impaired at the time of the offence.

In most Australian jurisdictions, once the defence is raised and supported by prima facie evidence, the burden shifts to the prosecution to disprove the defence beyond reasonable doubt. This ensures that individuals are not wrongly convicted if mental illness affected their capacity to understand or control their actions.

To present this defence, the legal team must:

• Obtain comprehensive psychiatric evaluations from qualified mental health professionals.

• Compile medical records and history of mental illness.

• Call expert witnesses to testify about the accused’s condition at the time of the offence.

• Cross-examine opposing experts if necessary.

Courts consider all evidence; medical, behavioural, and factual, before making a determination.

Legal Outcomes if the Defence is Successful

If the court accepts the mental illness defence, the accused is typically found “not guilty by reason of mental impairment.” This is a special verdict that acknowledges the offence occurs, but that the accused lacked criminal responsibility due to their mental condition at the time.

This outcome does not result in a standard acquittal or immediate release. Instead, the court must determine an appropriate response to protect both individual and the public. The available options vary by state but commonly include:

• Detention is psychiatric facility: the accused may be committed to a secure mental health institution for treatment and ongoing assessment.

• Supervision orders: These allow for conditional release into the community under strict mental health and behavioural supervision.

• Unconditional release: In rare cases where the risk to the public is minimal, the court may order the person’s release without conditions.

Limitations and Challenges of the Mental Illness Defence

When Necessity Does Not Apply

The Mental Illness Defence may be rejected by the court even if the accused has a diagnosed mental condition. The defence only applies if the illness meets the legal standard of mental impairment, and if it can be shown that the condition significantly affected the person’s capacity at the time of the offence.

• Conditions that Don’t Meet the Legal Definition: Not all mental health condition qualifies. Disorders such as mild depression, anxiety, or personality disorders may not reach the threshold unless they cause a complete inability to understand the nature or wrongfulness of the conduct. Similarly, voluntary intoxication does not qualify unless it results in a long-term mental illness.

• Partial Awareness of Actions: If the accused showed signs of understanding or control; such as planning the offence, hiding evidence, or fleeing the scene, the court may rule that they knew what they were doing, and reject the defence.

• Temporary Mental Conditions vs. Long-term Illness: Courts carefully distinguish between short-term impairments (e.g. intoxication-induced psychosis) and ongoing psychiatric disorders. Only long-standing mental illnesses that affect legal responsibility will generally support this defence.

Common Misconceptions About the Defence

There are several widespread misunderstandings about the Mental Illness Defence in Australian criminal law. One common myth is that its an “easy way out” for avoiding punishment. In reality, individuals found not guilty by reason of mental impairment are often subject to indefinite detention in secure psychiatric facilities, sometimes for longer periods than a prison sentence would have lasted.

Another misconception is that any mental illness qualifies for this defence. In truth, only severe, medically recognised conditions; such as schizophrenia or psychosis, that impair a person’s ability to understand or control their actions meet the legal standard.

It’s also incorrect to assume that this defence results in a full acquittal. While the person is not convicted in the usual sense, the court can impose supervision orders, mandatory treatment, or detention, depending on the perceived risk to the community.

Mental Illness Defence Laws in Different Australian States

NSW, Victoria & Queensland

The Mental Illness Defence is recognised in NSW, Victoria, and Queensland, but each state has its own legal framework and terminology.

• New South Wales: In NSW, the defence is governed by Section 38 of the Mental Health and Cognitive Impairment Forensic Provisions Act 2020 (NSW). The test requires proof that due to a mental illness, the accused did not know the nature and quality of the act, or did not know it was wrong. If successful, a verdict of “not criminally responsible by reason of mental health impairment” is returned.

• Victoria: Victoria uses the term “mental impairment” and outlines the defence under Section 20 of the Crimes (Mental Impairment and Unfitness to be Tried) Act 1997 (VIC). The test is functionally similar to NSW, and if successful, the accused is found “not guilty because of mental impairment” and may be subject to supervision or hospitalisation.

Other States & Territories

• Western Australian (WA): In WA, the defence is governed by Section 27 of the Criminal Code Act Compilation Act 1913 (WA). A person is not criminally responsible if, at the time of the offence, they were affected by insanity to the point they did not understand the nature or wrongfulness of their actions. Unique to WA, the Mentally Impaired Accused Review Board to oversees post-verdict detention and supervision.

• South Australia (SA): SA outlines the defence under the Criminal Law Consolidation Act 1935 (SA). A person may be found mentally incompetent if they mentally impaired and lacked capacity to understand or control their conduct. SA also requires the court to consider supervision orders post-verdict.

• Tasmania (TAS): In Tasmania, the defence applies where a mental illness prevented the accused from knowing their conduct was wrong. The court can impose indefinite detention or supervision.

• Northern Territory (NT): The NT recognises the defence under Section 43C of the Criminal Code Act 1983 (NT). If successful, the court may issue a custodial supervision order, reviewed periodically by the Mental Health Review Tribunal.

• Australian Capital Territory (ACT): In the ACT, the defence is outlines in Section 28 of the Criminal Code 2002 (ACT). It allows for supervision, detention, or conditional release based on risk assessments.

Why Expert Legal Representation is Crucial in Mental Illness Defence Cases

Successfully raising the mental illness defence requires a deep understanding of both criminal law and forensic psychiatry. It is not enough to show that the accused has a mental illness; lawyers must prove that the condition meets the strict legal criteria for mental impairment and that is directly affected the person’s criminal responsibility at the time of the offence.

This involves sourcing qualified psychiatric experts, obtaining and interpreting complex medical reports, and presenting a legally sound argument in court.

At Faraj Defence Lawyers, we specialise in defending clients where mental illness is a central issue. Our team has the experience to coordinate expert assessments, compile persuasive evidence, and advocate for outcomes that reflect your circumstances; ensuring your rights and mental health are properly considered throughout the legal process.

Need Legal Help? Contact Faraj Defence Lawyers

If you or a loved one is facing criminal charges where mental illness may be a factor, it’s essential to seek expert legal advice as early possible. Navigating the complexities of the mental illness defence requires both legal knowledge and a deep understanding of psychiatric evidence. 

At Faraj Defence Lawyers, we have extensive experience handling cases where mental health plays a central role. We work closely with leading mental health professionals, thoroughly examine all medical and legal aspects of your case, and ensure your defence is presented with clarity, accuracy, and care.

Contact Faraj Lawyers for a confidential and expert legal support tailoured to your circumstances.