The Act, which became law on Wednesday, makes the process easier for people to change the sex recorded on their birth certificate.
Millers Flat author Kyle Mewburn, who identifies as transgender, said the decision was a great step forward.
Ms Mewburn said the ability to change a birth certificate to have information that was correct from the individual’s perspective was important.
If she was a New Zealander she would want to put "F" on her birth certificate.
"I know who I am and why should everyone else keep questioning that."
Gender expression and gender reality was personal, she said.
Ms Mewburn said it was a fundamental human right to be able to fix mistakes.
"Your birth certificate is a mistake if you are trans, your issued birth certificate is a mistake."
It was not done on purpose, but being able to fix a bureaucratic error later in life was important, she said.
As an Australian citizen she had recently applied for a new passport.
"The first one since my transition and I’m slightly miffed I can only be an ‘X’.
"It makes me feel like I am an unknown creature or quantity which is a bit disappointing, so I am just so stoked that New Zealand is ahead of the game again, beating the Aussies at important social change."
Her preference would be being able to classify herself as female but that was not an option for her at present.
"I can only have ‘X’ unless I have gender reassignment [surgery]."
Internal Affairs Minister Jan Tinetti said it was a proud day in New Zealand history that Parliament had voted in favour of inclusivity and against discrimination.
"The passing of the Births, Deaths, Marriages, and Relationship Registration Bill brings with it a more accessible and inclusive process for people to change the sex recorded on their birth certificate.
"This law change will make a real difference for transgender, non-binary, takatapui and intersex New Zealanders."
