Australia's first ever same-sex marriages will take place from Saturday, after the High Court reserved its decision on the Commonwealth's challenge to ACT's same-sex marriage laws.

The court says it will hand down its decision next Thursday, and in the meantime will allow same-sex marriages to take place in Canberra.

The Commonwealth is challenging the validity of the ACT's same-sex marriage laws, which were passed in late October by the ACT Legislative Assembly.

The principal question in the case is whether the law is inconsistent with the Federal Marriage Act.

ACT Attorney-General Simon Corbell says marriages can take place this weekend because the Commonwealth did not seek an injunction.

"I'm sure couples will welcome the fact that the law will come into operation and that they can marry under the law, albeit, with the prospect that there is some risk to those ceremonies because of the uncertainty surrounding the High Court case until we receive the court's judgement," he said.

The ACT Government says 47 couples have lodged papers to get married.

Ivan Hinton from Australian Marriage Equality and his partner Chris Teoh, who are planning to get married on Saturday, were present at the hearing.

Mr Hinton says he knows of 12 other couples who will tie the knot.

On Tuesday, the Commonwealth Solicitor-General told the High Court that marriage is the union between a man and a woman.

Justin Gleeson told the High Court that the Federal Parliament has the right to define marriage in Australia.

He says that marriage is a common genus that is not divisible into multiple species.

However, the ACT is arguing that same-sex marriages can coexist alongside the more traditional form of marriage.

Australian Marriage Equality's lawyer Anna Brown says the ACT Government should have the right to legislate for same-sex marriages.

"The ACT sought to argue that the ACT marriage laws should be held to be valid because it governed only same-sex relationships and that wasn't in conflict with the Federal Marriage Act," she said.

Recently, a similar bill in Tasmania was defeated and a bid by the New South Wales Upper House to legalise same-sex marriage was lost by a single vote.

Businesses are also set to benefit; Kate Dawson, from Flint on the Vines, says she has had numerous marriage inquiries and one booking.

"I have looked into our figures and I predict it should help to increase ours by about 20 per cent," she said.