Four years after the androgynous Sydneysider first applied to the NSW Registrar of Births Deaths and Marriages to be registered as ''sex: non-specific'' the High Court had determined that the Registrar must do exactly that.

''If some people are granted the right to have their sex recognised and to have the benefits that come from that, why can't everyone have that?'' the Redfern resident said.

In a decision with far reaching implications for individuals and institutions across the country, the High Court on Wednesday unanimously upheld a previous decision that people like Norrie should be allowed to register as neither male nor female on basic documents such as birth certificates.

The decision is recognition by the highest court in the land that sex is not only male or female and this should be recognised by the law.

Norrie, a keen swimmer who rides a bike with its own bubble maker, was born with male physical characteristics but, following gender reassignment surgery, now has male and female characteristics and identifies as neither.

After granting Norrie the ''non-specific'' designation in 2010, the NSW Registrar reversed its decision. Two subsequent legal challenges by Norrie were unsuccessful. In May last year, represented pro bono by Sydney law firm DLA Piper, a third challenge was successful in the NSW Court of Appeal.

The Registrar appealed to the High Court which has now delivered a judgment in no uncertain terms, accepting the argument of Norrie's legal team, led by former Howard government solicitor-general, David Bennett, QC.

Counsel for the Registrar had argued that the acceptance of more than two categories of sex would cause ''unacceptable confusion''. But the five-judge panel rejected this argument.

''For the most part, the sex of the individuals concerned is irrelevant to legal relations,'' their judgment says.

The judges said the Commonwealth Marriage Act was ''the chief, perhaps the only, case where the sex of the parties to the relationship is legally significant''.

They found ''evident force'' in Norrie's argument that to classify her as male or female while her sex remained ambiguous would be to record misinformation in the register.

The decision has particular ramifications for Victoria and Queensland, which have similar legislation to the NSW Births Deaths and Marriages Act - the law at the centre of Norrie's legal contention.

These states are likely to be bound by the High Court's decision, while other states must regard it as persuasive precedent if similar situations arise.

Advocates for transgender, intersex and androgynous people said it was likely others like Norrie would seek to have their birth certificates changed to include the non-specific designation. This designation could also be available to babies who are born with ambiguous sexual characteristics.

Samuel Rutherford from A Gender Agenda said the decision was ''a powerful affirmation''.

Norrie expressed the hope that the decision would lead to greater acceptance and understanding.

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