Celebrant Judy Aulich will have her hands full with nine same-sex marriages in about 48 hours from Saturday morning, plus two heterosexual ceremonies, but said most of her couples were after a simple event.

"Overwhelming the couples I'm doing are what I'm calling 'quickies' – they've been in relationships for a long time and they just want the ceremony," Ms Aulich said.

Dress codes will vary greatly, but most will be done within 30 minutes, with six of the nine couples tying the knot in small events at Ms Aulich's Giralang home.

"One couple rang me and said they'll be coming in their jeans ... another said they were going to book a hotel room and were going to do it in bed in their pajamas," she said.

"The celebrant code is that you sort of take your code from the couple – I might end up in [my] dressing gown."

The two other couples were expected to have 70 to 80 people at their ceremonies at the National Arboretum's Margaret Whitlam Pavilion and the shore of Lake Burley Griffin, she said.

The formalities of the ceremony will differ little from a traditional marriage. There'll be a registered celebrant, rings can be swapped, and the couple will sign a marriage certificate witnessed by two people.

The ACT government's standard template indicates each party will commit to take their partner as their lawful wedded spouse, husband or wife, as they prefer.

Instead of the celebrant's mandatory description under Commonwealth law of marriage as a union between a man and a woman, the official will refer to their authority (challenged but not as yet removed by the High Court) under the ACT law to solemnise marriages, with no reference to gender required.

Ms Aulich said she would be guided by the couples as to how she encourages the first matrimonial smooch, with "you may now have a kiss" one option.

"It will now be appropriate to say 'you may now kiss your wives'," she said.

"My marriage ceremonies for same sex couples mirrors my ceremonies for a heterosexual couple – their mandatory statements are slightly different, but basically the same."

Emily Jehne said her Sunday wedding to partner Ellie would be a smaller affair than their civil partnership five years ago.

"There was a lot of uncertainty with the High Court case – we didn't want to pay big deposits for dresses and everything," Ms Jehne said.

The Canberra couple had about 60 people at their earlier ceremony at the Rose Garden at Old Parliament House, with white dresses, a photographer and bridesmaids, but expect two witnesses and "maybe another five to ten more" on the weekend at Ms Aulich's home.

Celebrant Julie Rattenbury attended the High Court hearing on Tuesday and said Saturday – where she will officiate over three same-sex marriages – promised to be a thrilling day.

"We were all thinking [the court] would make their decision before the weekend – so we've got a lot of work to do, but it's exciting," Ms Rattenbury said.

There are 47 couples who have given the required one month's notice to be eligible to marry under the ACT law from Saturday.

Same-sex newlyweds will be able to keep their marriage certificates, even if a High Court ruling finds their union legally invalid.

A legal certificate can be issued by the register following same-sex marriages conducted across Canberra this weekend, under the Marriage Equality (Same Sex) Act.

These certificates can be used for legal purposes, but may be deemed void if the High Court rules against the law on Thursday.

A Justice and Community Safety Directorate spokeswoman said legal certificates would no longer be issued if the High Court found the law ineffective, but those issued before the decision would not be recalled.

“The Registrar-General is not expressly required by law to recall marriage certificates issued before the High Court decision,” she said.

“However, these certificates would not have legal effect, so could subsequently not be used, for example, to change name.”

The Office of Regulatory Services developed three new types of certificates for same-sex marriages, including a ceremonial certificate to be provided to the couple on the day.

An official certificate duplicate book will be provided for authorised celebrants and a commemorative certificate that can be purchased by couples after their marriage is registered.

Celebrants have a fortnight to provide paperwork to the Office of Regulatory Services after the wedding, but a legal certificate can be produced on the spot once the forms are received.

The number of authorised celebrants in the ACT doubled following the introduction of marriage equality laws, from 41 Civil Union Celebrants to 80 Authorised Celebrants.

Specific wording was provided to authorized celebrants, including mention of the “solemn and binding nature of the relationship” couples are entering.

“Under the law, this wedding recognises that you are voluntarily entering into a lawful and binding union, for life, to the exclusion of all others,” it reads.

Changes were also made to the Births, Deaths and Marriages Register to provide for marriages under the new laws to be registered.