A criminal court can consider the accused's mental illness as a defence, since Section 84 of the Indian Penal Code (now reflected under the Bharatiya Nyaya Sanhita) provides that an act done by a person of unsound mind, incapable of understanding the nature of the act or that it was wrong, does not constitute an offence. Whether a criminal court can consider the accused's mental illness as a defence successfully depends on establishing, through credible medical and psychiatric evidence, that this specific standard of incapacity existed precisely at the time the offence was committed, not merely a general diagnosis of mental illness. This precise timing requirement is often the most challenging aspect of the defence, since it is not enough to show the accused suffers from a mental illness generally — the incapacity must be shown to have existed at the exact moment the act took place.

Courts apply what is often called the McNaughton test, adapted into Indian jurisprudence, focusing narrowly on whether the accused, due to unsoundness of mind, was incapable of knowing the nature of the act or that it was wrong or contrary to law. This is a legal standard, distinct from a purely clinical psychiatric diagnosis, meaning that a person can have a recognised mental illness and still not meet this specific legal threshold if they retained sufficient understanding of their actions at the relevant time.

This defence requires substantial expert evidence and careful legal presentation to succeed, typically including psychiatric assessment as close in time to the offence as possible, medical history documenting the illness and its progression, witness accounts of the accused's behaviour and mental state around the time of the incident, and expert testimony connecting all of this to the specific legal standard required. Building this evidentiary foundation takes time and careful coordination between legal counsel and medical experts.

For assistance building a mental illness defence supported by proper medical documentation, Aapka Legal Advice can guide you through this sensitive process, from identifying the right experts to presenting the evidence in the manner courts expect. Our network of Top Criminal Lawyers in India and retired judges panel have handled numerous cases involving this nuanced and important defence, understanding exactly how to bridge the gap between medical evidence and the specific legal standard courts apply. In conclusion, mental illness can absolutely form a valid legal defence, but success depends heavily on precise, well-documented evidence connecting the illness to the specific moment of the alleged offence.