Galloway and West Dumfries MSP Finlay Carson believes the joint two-port approach could have all the attributes necessary to be successful in the bidding process.
He said: “Given the importance of the ports at Cairnryan and Belfast both locally and nationally it makes complete sense that it should be given serious consideration now that the bidding process has opened up.
“Cairnryan is not only the gateway to Ireland for Scottish and UK goods but, crucially, Europe and that is why I think it stands a very good chance of being selected. I firmly think linking its bid alongside Belfast could be a winner.
Mr Carson hopes local bodies and organisations will also unite behind the bid.
He added: “I hope the potential Cairnryan-Belfast collaboration will get the active backing of local businesses and organisations as the economic benefits as well as new jobs are critical in the long-term future of the south west of Scotland.
“Everything possible should be done to convince both governments that this investment is desperately needed here.”
Both the UK and Scottish governments set out their shared vision for what Green Freeports in Scotland should look like last week.
It is hoped that the freeports will regenerate local areas, create high quality jobs and support the transition towards a net zero economy.
Mr Carson has written to the chief executive of Dumfries and Galloway Council, who will be leading the bid, as well as the South of Scotland Enterprise to unite behind the joint collaboration.
He has also approached the lead group in Ireland to ask that they also explore the potential of proposing a Cairnryan-Belfast bid in order to strengthen the chances of gaining freeport status.
Interested bidders now have 12 weeks to assess and prepare their bids, which will then be appraised by government officials, with ministers having an equal say on the final selection.
It is expected that the successful Green Freeport locations will be announced in early autumn 2022, beginning operations in spring 2023.