"Most people do not think that sex is only for marriage and the vast majority of couples in Australia who marry live together first," he wrote in an opinion piece for Fairfax Media published on Monday evening. "Many Australians are not convinced that marriage should be for life."

When asked why it was gay marriage, rather than no-fault divorce or pre-marital sex, that had prompted the church to consider refusing to participate in marriage laws, he said he was not around in 1975 when no-fault divorce was introduced.

"I do think there are a lot of Christian people who see the same-sex marriage issue as the big issue," he said. "For me, it's really one more step along what has really been a long process over the past few decades."

He said if the marriage act was changed it would have no effect on Presbyterians, as they followed the teachings of Jesus on marriage, rather than secular laws, "but we would think that leaving the Marriage Act is a way to make that position as clear as possible".

Last month, Canberra couple Nick and Sarah Jensen faced a community backlash after Mr Jensen announced the couple would divorce if same-sex marriage was allowed.