A MARRIAGE is a sworn, binding contract that can only be broken in a Family Law court.

Couples who are married become each others' next of kin.

Unlike a de facto relationship, a legal marriage offers equal protection under the law, such as joint property and inheritance rights, rights to benefits and insurance.

For a foreign partner marrying an Australian, a legal marriage also affords them citizenship rights under the Constitution.

The rights of a partner cannot be denied by a blood relative, such as parental rights should a same-sex couple choose to adopt.

Under a marriage, if a child is conceived by IVF, both spouses are automatically legal parents, whereas under a de facto relationship, parentage depends on whether that relationship can be proven to exist.

In all circumstances, partners in a de facto relationship are required to provide more proof of their relationship.

Examples of this burden of proof include:

If their partner has died and they need to be listed as their spouse on the death certificate or involved in funeral planning (being listed on a death certificate is vital when it comes to superannuation payouts and other issues)

If their partner has died without leaving a will

If their partner is gravely ill and they must make decisions about their care and treatment

A de facto relationship is also defined differently in different scenarios.

For Centrelink purposes, a de facto relationship begins from the time you start living together, while under migration law it begins after 12 months of cohabiting, unless you have a child together or de facto relationships are illegal in your country of origin.

Under family law, couples must have lived together for a minimum of two years, unless they have a child together or have registered their relationship to be considered de facto partners.

The Marriage Act was changed in 2004 by then Prime Minister John Howard, to include to a definition of marriage as the "voluntarily entered-into union of a man and a woman to exclusion of all others”.

Prior to this the act did not define marriage.

At the time, Howard told reporters the decision to insert the definition into the legislation was "to make it very plain that that is our view of a marriage and to also make it very plain that the definition of a marriage is something that should rest in the hands ultimately of the parliament of the nation.”

"(It should) not over time be subject to redefinition or change by courts, it is something that ought to be expressed through the elected representatives of the country,” he said.

Queensland has legislation permitting same sex couples to register domestic relationships.

To register, you must prove that you meet the criteria, such as by demonstrating "personal or financial commitment and support of a domestic nature for the material benefit of the other.”

These relationships are not reliably recognised overseas.