Religious leaders from several faiths will launch the campaign on Tuesday to coincide with a pre-COP summit in Fiji, where governments will discuss priorities for November's United Nations climate conference.
The group, along with representatives from climate and policy organisations, says Australia has an opportunity to lead the world on climate action at the event and cannot afford to squander it.
Pre-COP31 events in Fiji and Tuvalu expected to attract thousands of participants are designed to identify common ground on emissions reductions and climate finance while highlighting challenges facing Pacific nations.
Leaders from Christian, Muslim, Buddhist, Sikh and other faiths will show their support at locations from Cairns to Perth on Tuesday, Australian Religious Response to Climate Change executive director Tejopala Rawls said.
The group would also issue an open letter to Prime Minister Anthony Albanese, he said, calling for Australia to support a global fossil fuel treaty and a planned phase-out of coal, oil and gas.
"Australian churches and faith communities have got very strong connections in the Pacific so there was a very strong desire to stand in solidarity with our brothers and sisters in the Pacific and to try and reinforce what they've been saying on this issue," he told AAP.
"What we're doing is saying we need this to be on the agenda - Australia has a responsibility to lead."
Australia had made significant progress cutting emissions domestically, Mr Rawls said, but it and other nations needed to address fossil fuel exports to make a meaningful difference to global warming.
"The question of phasing out fossil fuels is one that can tend to polarise people," he said.
"What we need is a plan that does that in a co-ordinated way internationally where nobody's needs get left out and nobody gets left behind."
Representatives from groups including Oxfam, Greenpeace, The Australia Institute and ActionAid will also attend the event in Nadi.
Make Big Polluters Pay campaign strategic lead Julie-Anne Richards said Australia should seize the opportunity to invest more in climate action.
"This pre-COP event is an opportunity to show leadership and encourage other countries to follow rather than talking about other countries taking action and waiting for them," she said.
"We need to get out there, in front."
Climate finance would be a major topic for discussion at the event, she said, with the United Nations' loss and damage fund facing a shortfall and a Pacific climate fund yet to reach its $US500 million target.
Australia has committed $100 million to the fund.
"Australia needs to step up more and increase the amount that it is going to contribute to the Pacific Resilience Facility as a member of the Pacific family, and as by far the biggest climate polluter in the region," she said.
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