The legislation which deals with Self-defence is the Criminal Code Act 1913 at Section 248. It provides as follows:
(1) In this section —
harmful act means an act that is an element of an offence under this Part other than Chapter XXXV.
(2) A harmful act done by a person is lawful if the act is done in self-defence under subsection (4).
(3) If—
(a) a person unlawfully kills another person in circumstances which, but for this section, would constitute murder; and
(b) the person’s act that causes the other person’s death would be an act done in self-defence under
subsection (4) but for the fact that the act is not a reasonable response by the person in the circumstances as the person believes them to be,
the person is guilty of manslaughter and not murder.
(4) A person’s harmful act is done in self-defence if —
(a) the person believes the act is necessary to defend the person or another person from a harmful act, including a harmful act that is not imminent; and
(b) the person’s harmful act is a reasonable response by the person in the circumstances as the person believes them to be; and
(c) there are reasonable grounds for those beliefs.
(5) A person’s harmful act is not done in self-defence if it is done to defend the person or another person from a harmful act that is lawful.
(6) For the purposes of subsection (5), a harmful act is not lawful merely because the person doing it is not criminally responsible for it.