Christian church leaders remain at the forefront of organised opposition to the legalisation of same-sex marriage. But Mr Munson, a Canberra Uniting Church minister, is a registered celebrant under the ACT's marriage equality law and will preside at the wedding of a male couple this weekend.

He has organised commitment ceremonies for same-sex couples in the past and said he was happy for gay and lesbian couples to marry.

"Jesus never said anything about it [same-sex marriage] and he was one who welcomed all people, regardless of their circumstances,'' he said.

Mr Munson, a former minister at St James church in Curtin, is now working as a social worker but also acts as a locum minister.

His lack of attachment to a parish had made celebrating same-sex marriages easier because of the continuing debate about gay marriage within the Uniting Church.

Mr Munson said marriage had evolved and same-sex couples should be able to express their love for each other.

"I think it comes down to an understanding of the Bible,'' he said. "[It] was written in different times and so they had different understandings of the world around them. We've become more knowledgeable.

''There's nothing simple about being homosexual or gay. It's just who people are."

Mr Munson said he was able to individualise the format of marriage ceremonies to meet the needs of couples. "It could be a simple civil ceremony through to an expression of any faith tradition. It all falls within the service pro forma that we're supplied with by the government,'' he said.

Many same-sex couples are expected to marry this weekend under the ACT's same-sex marriage law, though they maybe short-lived marriages as the High Court of Australia will rule on the constitutionality of the law on Thursday.

Senior Christian, Muslim and Jewish leaders have urged the ACT Legislative Assembly to vote against introducing Australia's first same-sex marriage scheme.