The Australian Capital Territory becomes the first Australian jurisdiction to legalize same-sex marriage with the Marriage Equality (Same Sex) Act 2013

The Marriage Equality (Same Sex) Act 2013 was an act of parliament of the Australian Capital Territory Legislative Assembly that was intended to legalise same-sex marriage in the Australian Capital Territory (ACT). It was first presented to the ACT Legislative Assembly on 19 September 2013 by the ACT Attorney-General, Simon Corbell. The law intended to build on the existing recognition of same-sex unions in the Australian Capital Territory, which included recognition of de facto partners, civil partnerships and same-sex-only civil unions (with civil unions being replaced by same-sex marriage if the Act was successfully passed). The act was passed in the Legislative Assembly on 22 October 2013. It came into operation on 7 November although wedding ceremonies under the provisions of the Act did not occur until 7 December 2013.West Australian parliamentarian Stephen Dawson and his husband Dennis Liddelow were the first same-sex couple to marry under the new laws. Upon the law's commencement, the Abbott Government challenged the legal and constitutional validity of the Act, lodging an immediate challenge in the High Court of Australia. The case was heard on 3 December and a ruling was handed down on 12 December 2013. The High Court unanimously struck the act down in its entirety, on the basis that it was in conflict with the federal Marriage Act, which defined marriage in Australia as the union of a man and a woman. The court did however expressly confirm in its ruling that the Parliament of Australia had the constitutional authority to amend the definition of marriage in the Marriage Act, so as to allow same-sex couples to marry.

The Australian Capital Territory (commonly abbreviated as ACT), known as the Federal Capital Territory (FCT) until 1938, is a landlocked federal territory of Australia containing the national capital Canberra and some surrounding townships. It is located in southeastern Australian mainland as an enclave completely within the state of New South Wales. Founded after Federation as the seat of government for the new nation, all important institutions of the Australian Government are headquartered in the territory.

On 1 January 1901, federation of the colonies of Australia was achieved. Section 125 of the new Australian Constitution provided that land, situated in New South Wales and at least 100 miles (160 km) from Sydney, would be ceded to the new federal government. Following discussion and exploration of various areas within New South Wales, the Seat of Government Act 1908 was passed in 1908 which specified a capital in the Yass-Canberra region. The territory was transferred to the federal government by New South Wales in 1911, two years prior to the capital city being founded and formally named as Canberra in 1913.

While the overwhelming majority of the population reside in the city of Canberra in the ACT's north-east, the territory also includes some surrounding townships such as Williamsdale, Naas, Uriarra, Tharwa and Hall. The ACT also includes the Namadgi National Park which comprises the majority of land area of the territory. Despite a common misconception, the Jervis Bay Territory is not part of the ACT although the laws of the Australian Capital Territory apply as if Jervis Bay did form part of the ACT. The territory has a relatively dry, continental climate experiencing warm to hot summers and cool to cold winters.

The Australian Capital Territory is home to many important institutions of the federal government, national monuments and museums. This includes the Parliament of Australia, the High Court of Australia, the Australian Defence Force Academy and the Australian War Memorial. It also hosts the majority of foreign embassies in Australia as well as regional headquarters of many international organisations, not-for-profit groups, lobbying groups and professional associations. Several major universities also have campuses in the ACT including the Australian National University, the University of Canberra, the University of New South Wales, Charles Sturt University and the Australian Catholic University.

A locally elected legislative assembly has governed the territory since 1988. However, the Commonwealth maintains authority over the territory and may overturn local laws. It still maintains control over the area known as the Parliamentary Triangle through the National Capital Authority. Residents of the territory elect three members of the House of Representatives and two senators.

With 431,215 residents, the Australian Capital Territory is the third smallest mainland state or territory by population. At the 2016 census, the median weekly income for people in the territory aged over 15 was $998, significantly higher than the national average of $662. The average level of degree qualification in the ACT is also higher than the national average. Within the ACT, 37.1% of the population hold a bachelor's degree level or above education compared to the national figure of 20%.