Births, Deaths, Marriages, and Relationships Registration Act 1995, s 9
If the child’s parents are legally married to each other, or in a civil union or de facto relationship with each other, both parents sign the birth registration form, which is then given to the registrar of Births, Deaths and Marriages.
If a registrar is satisfied that a child has only one parent, or the other parent is unavailable, or it would be too distressing otherwise, only one parent has to sign the birth registration form.
If a man was not married, in a civil union or de facto relationship with the mother of a child any time between the conception of the child (when the woman became pregnant) and the birth of the child, he can only be named on the child’s birth certificate if he:
Births, Deaths, Marriages, and Relationships Registration Act 1995, s 15
signed the birth registration form with the mother, or
gave written permission, also signed by the mother, to put his name on the birth certificate, or
signed the birth registration form on his own because the mother was unable to sign. This could be because she was dead, or missing, or of unsound mind, or unable to act because of a medical condition, or
the Family Court made a Paternity Order, or guardianship order in his favour stating that he should be named on the child’s birth certificate
has been declared by the Family Court or the High Court to be the father of the child. See “Declaration of paternity” in this section