The Cop26 Coalition said the Democrat had donated $10,000 (£7,250) to the fund and urged others to take action.
The UN climate conference starts in Glasgow on Sunday, but the coalition said about 100 delegates from frontline and indigenous global south communities are struggling to be able to attend, despite being accredited.
This is being blamed on a combination of the high cost of accommodation, Covid-19 travel curbs and quarantine rules.
The campaign group has joined with Climate 2025, the Climate Emergency Fund, Youngo (a global network of young activists) and activists Fridays for Future Most Affected Peoples and Areas, to launch the fundraiser to help those affected make their voices heard at the talks.
Ms Ocasio-Cortez said: “It’s vitally important that those areas most affected by climate change have representatives at Cop26.
“Unfortunately, it is these very activists that have the least access.
“I’m committing to support two international advocates to attend the conference, and I challenge my colleagues in (the US) Congress and in wealthier nations around the globe to step up to ensure these 90 activists have a chance to be heard.”
The funds raised will go to covering travel, accommodation, any quarantine requirements and other necessary costs for those able to attend in person. The costs are said to range from £3,250 to £6,500.
Those unable to travel will be supported through funding items such as the rental of virtual meeting rooms and any domestic travel needed to participate remotely.
The Cop26 Coalition has been working since May to support hundreds of activists with the immigration process.
Rachael Osgood, the coalition’s lead immigration coordinator, said: “The immigration service at the Cop26 Coalition has supported hundreds of people from frontline and indigenous global south communities who are trying to make it to Cop26.
“From all of our work, one thing is clear: due to compounding structural barriers, thousands are being silenced.
“And these thousands represent millions who are already fighting for their lives on the front lines of the climate crisis. The time to act is now.”