The Marriage Act 1961 (Cth) provides that any person who, while married, goes through a form or ceremony of marriage with any other person is guilty of an offence [s 94(1)].

Maximum Penalty: 5 years imprisonment

It will be a defence if the accused person can show reasonable grounds for having believed that he or she was not married.

It is also a defence to prove, on the balance of probabilities, that the spouse had been absent for such a time and in such circumstances as to provide reasonable grounds for presuming that the spouse was dead and also that the person believed that his or her spouse was dead. It is enough for the first part of the defence if the accused can prove that the spouse had been continually absent for seven years and that the accused had no reason to believe that the spouse was alive in that period of seven years [see s94(2)-(3)].

The Act also provides that any person who goes through a form or ceremony of marriage with a person who is married is guilty of an offence if the accused knows, or has reasonable grounds to believe, that the other person is married [s 94(4)].

Maximum Penalty: 5 years imprisonment

There is an exemption for those people who wish to go through a form or ceremony of marriage with each other more than once [s 94(5)].

The spouse of the accused can be forced to give evidence in a bigamy case, but that evidence alone is not enough to establish that the accused was married at the time of the offence [ss 94(6)-(7)].