A Sydneysider has won a High Court case to be recognised as gender-neutral.

Norrie, who was born male but underwent gender reassignment to become a woman, identifies neither as male or female and has taken legal action against NSW's Registry of Births, Deaths and Marriages to be granted a non-specific certificate.

The court was asked to consider whether "non-specific" can be included as a third gender category under the Registry's Act.

"The act recognises that a person may be neither male nor female, and so permits the registration of a person's sex as 'non specific'," read the High Court judgment, handed down on Wednesday.

Norrie, who goes by one name, was famously granted a world-first non-specific status in 2010, but months later the NSW government revoked the classification.

The matter was challenged by both Norrie and the Registry until the latter took an appeal to the High Court.

Lawyers for the Registry argued that unacceptable confusion would flow from the acceptance of more than two gender categories, and that the purpose of a reaffirmation procedure is to assist a person to be considered a member of the opposite sex.

Norrie stopped taking hormones after surgery, preferring to live as neither male nor female.

Counsel for Norrie said it is the register's purpose to record the truth.

"Norrie's sex remained ambiguous so that it would be to record misinformation in the register to classify her as male or female," a judgment summary reads.

Sitting in Canberra on Wednesday, the bench unanimously found in favour of Norrie.

"The act does not require that people who, having undergone a sex affirmation procedure ... must be registered, inaccurately, as one or the other," the court found.

Norrie's application for non-specific status should now be reconsidered by the Registry in accordance with the court's finding, the judgment said.

The Registry must pay Norrie's costs of the High Court appeal.

Norrie said other people wanting to identify as a non-specific gender had made contact.

"Many other people let me know they wanted do that (identify as non-specific) in Australia and indeed around the world," Norrie told reporters in Sydney.

"Maybe people will understand there's more options than the binary."

Norrie's solicitor, Scott McDonald, said the decision was likely to have similar repercussions in Queensland and Victoria, which have similar state legislation to NSW.

"It'll be binding on the states that have identical or similar legislation" he told reporters.

And for states such as Western Australia, with very different legislation, the judgment has sent a message the High Court doesn't think gender is limited to male and female.

Norrie was born a man in Scotland and had gender reassignment surgery in the late 1980s.

Norrie said the legal battle had taken a personal toll, but it was the lawyers who had done most of the hard work.