[2] It came into operation on 7 November although wedding ceremonies under the provisions of the Act did not occur until 7 December 2013.

It was, however, opposed by all eight members of the Liberal Opposition, who argued that same-sex marriage should be dealt with by the Federal Parliament only.

Further proposed amendments to the bill that would have created a separate institution of marriage for same-sex couples were rejected by the ACT Government.

[3] It was at that point same-sex couples could officially notify of their intention to marry, allowing them to arrange weddings commencing 7 December 2013.

The Commonwealth Constitution, section 51(xxi), provides the federal parliament with power to make laws with respect simply to "marriage".

In conventional terms of constitutional interpretation, one view can be that this is confined to different-sex marriage because that was all that the constitutional framers had in mind, while another view can be that "marriage" should be understood in terms of current public perceptions.

[citation needed] Already on 10 October, Commonwealth Attorney-General George Brandis stated that, if the ACT's bill were passed, the Commonwealth would challenge it in the High Court of Australia as inconsistent with the federal Marriage Act.

[18] However, the federal government could not have been confident that such legislation would pass, since it had a majority only in the House of Representatives and not in the Senate.

Shane Rattenbury and Labor Party MLAs released similar statements affirming their support for the bill.

[19] On 22 October 2013, as soon as the ACT had passed the bill, the Commonwealth Government requested a High Court hearing regarding the validity of this law.

Similarly, within and by reason of the schema of the Marriage Act, couples who are not man and woman (whether same-sex or intersex) are and must remain for the purposes of Australian law 'unmarried' persons.

manifest an intention to be an exhaustive or exclusive statement of the [Australian] law governing the institution of marriage".

[5]: para 60  The Court then found it unnecessary to consider inconsistency with the Family Law Act 1975.

To have stopped at that point, however, would have left the Commonwealth, the ACT and the states that have been contemplating same-sex marriage legislation in limbo as to what they might do next.

[citation needed] The Court rejected the conventional options in constitutional interpretation: Thus the word "marriage" in Constitution section 51(xxi) states a "topic of juristic classification" which is not tied to any historical model and the federal parliament can legislate as it wishes within that topic.

[citation needed] The Court did not refer to the several same-sex marriage ceremonies that had already taken place.

The most direct way to achieve that is to amend the Marriage Act, to provide that a person's sex is not a criterion of eligibility to marry.