A sperm donor who argues he should be considered the legal father because he was involved in the child's life has taken his case to the High Court .
The case comes down to whether or not state law should apply instead of Commonwealth laws.
The state law in question says a sperm donor isn't a parent.
But lawyers for Robert Masson, the man's court pseudonym, argue the state laws should not apply as there is no gap in the commonwealth law.
Under the commonwealth law Mr Masson is considered a parent, as he is the biological father and is involved in the child's life.
The case has its beginnings in late 2006, when Mr Masson and Susan Parsons (her court pseudonym) agreed to have a child through artificial insemination.
Mr Masson agreed on the understanding he would parent, provide financial support and financial care.
He is named as the girl's father on her birth certificate.
He was actively involved in the girl and her younger sister's life, with both calling him "Daddy".
Issues arose when the mother and her partner wanted to move to New Zealand with the girls.
Mr Masson stopped them through the Family Court as he was found to be a parent, but on appeal state laws were used to rule him as purely a sperm donor.
Solicitor General Stephen Donaghue QC argued in support of Mr Masson, saying the commonwealth definition should be used.
"State law is just not relevant," he told the court.
Lawyers for Ms Parsons and her partner say the man is a sperm donor and not a parent.
The hearing continues.