The managing director of the ACL Jim Wallace appeared at the House of Representatives same-sex marriage inquiry in Sydney this afternoon.

Mr Wallace was a witness to the  House of Representatives Standing Committee: Social Policy and Legal Affairs Committee along with a number of other family groups and churches.

Mr Wallace told the inquiry that marriage should only be changed if there were good reason too.

"I am saying that the biological issue here...the biological reality and truth of marriage is that we take - we create motherhood and fatherhood in that environment and we protect it and we encourage it," he said.

"Society and government - in its responsibilities to society - is to take this thing called marriage and to say what good does it give us?

"And one of those goods which for all the good intent in the world a homosexual couple can never be at the same time is a mother and father to a child. And I’m saying that concept needs to be protected by government. It’s government’s responsibilities to protect those concepts."

Mr Wallace told the inquiry that the value of family would be sacrificed in changing the definition of marriage.

"If it were discrimination - substantive discrimination - that you might choose to change this long held definition would be if you suddenly decided that your value of family or your value on motherhood and fatherhood was such that you were prepared to sacrifice it. I don’t believe governments should do that.

"I think for all the benefits marriage holds – for all the benefits its holds in its aspirations to the exclusions of all others - man and woman, biological parents, to the exclusion of all others for life – the benefit it holds to children – I think governments need to uphold it and it would need to be a really good reason to change it," he said.

Mr Wallace also had an opportunity to do an interview with SBS World News Australia about the ACL's concerns about legalising same-sex marriage.

The full transcript of the day will be published on in the next week.

The committee will now go and write a report based on the submissions and evidence received.

The next step in the debate over the future of marriage will be public hearings conducted by the Senate which is also inquiring into a Greens marriage bill.

This is likely to occur next month and a vote on the various same-sex marriage bills in the House of Representatives and the Senate will

likely take place in the spring.