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Criminal Defences (NSW)

A criminal defence is an argument used to justify the actions of a person charged with a criminal offence. A defence may be legal (such as self-defence) or factual (such as an alibi). Legal defences can be complete or partial. They all have their roots in the common law and some are now codified in legislation. Some offences have specific defences that apply to them and these are set out in the Crimes Act 1900. This article outlines criminal defences in New South Wales.  

Complete defences

The following can be argued as complete defences.

Claim of right

If a person charged with a stealing offence has a genuine belief that they (or someone else they are acting on behalf of) has a legitimate claim of right to the money or property allegedly stolen this it is a complete defence.

Honest and reasonable mistake of fact

Honest and reasonable mistake of fact is a defence to offences of strict liability (such as speeding). It applies where an accused had an honest and reasonable belief in a state of affairs which, if it existed, would mean that they were innocent of any offence. It does not apply if the mistake is a mistake of law.

Mental illness

If a person is severely impaired by mental illness, they may rely on this as a complete defence to criminal offences. For this to succeed the accused must prove that they did not understand ‘the nature and quality’ of their actions due to their mental illness. This means that they must prove that they either did not know what they were doing or that they didn’t understand that it was wrong.


If a person is charged with a violent offence such as assault or murder, they have a complete defence if they were acting in self-defence or in defence of another person. If the accused raises self-defence, it then becomes the responsibility of the prosecution to prove that they were not acting in self-defence.

For self-defence to succeed, the defendant must prove that they had reasonable grounds to believe that what they did was necessary in self-defence. The principle of proportionality is key to assessing this. The accused’s actions must have been proportionate to the threat faced as they perceived it.


The defence of necessity operates where circumstances cause a person to break the law to avoid serious consequences. This will only succeed if the accused can prove that they genuinely believed that what they did was necessary in response to an emergency situation. An example of where this may be argued is where a person speeds to get a seriously injured person to hospital before they die.


Duress is argued where an accused committed an offence only because of serious threats made to themselves or another person if they did not commit the offence. For this defence to succeed, the accused must show that they committed the offence only to avoid the threat being carried out.

Duress cannot be argued in relation to murder or manslaughter.


Consent is most often raised as a defence in sexual assault cases. A person is not guilty of sexual assault if the complainant consented to sex with them.

Consent may also be advanced as a defence in assault cases (ie the complainant consented to being assaulted – for example, in a fair fight). However, a person cannot consent to serious harm so this defence is not available in assault matters where the victim suffered serious injury.


While not a defence as such, an accused’s intoxication may be taken into consideration when assessing whether they had a specific intent. A specific intent offence is an offence where the prosecution must prove that the accused specifically intended to bring about a specific result. An example of this is maliciously inflicting grievous bodily harm with intent to inflict grievous bodily harm. To find a person guilty of this offence it isn’t sufficient for the prosecution to prove that grievous bodily harm was inflicted; it must also prove that it was intended to be inflicted. An intoxicated person might not be capable of having that specific intent.

Partial defences

Partial defences only apply to murder charges. These do not result in acquittal but lead to a conviction for the less serious offence of manslaughter. They lessen the offender’s culpability but do not excuse or justify their actions.


Provocation is based on a claim that the victim provoked the accused to the extent that they temporarily lost their power of self-control. It must be established that the victim’s actions would have caused any reasonable person to act as the accused did.

Diminished Responsibility

Diminished responsibility is based on a claim that the accused was suffering from an abnormality of the mind at the time of the alleged offence which substantially impaired their mental responsibility. This cannot be relied upon to excuse the accused if they were under the influence of drugs or alcohol at the time of the offence.

If you require legal advice or representation in any legal matter please contact Armstrong Legal. 

Michelle Makela

This article was written by Michelle Makela

Michelle has over 15 years experience in the legal industry, working across commercial litigation, criminal law, family law and estate planning.  Michelle has been involved in all practice areas of the firm and in her personal practice has had experience in litigation at all levels (State and Federal Industrial Tribunals, the Supreme Court, Court of Appeal, the Federal Court, Federal...

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