Then-foreign minister Simon Kofe said "we are sinking" in a 2021 video speech to the United Nations climate change summit, highlighting the plight of the low-lying country with a population of 11,000 where tides are predicted to cover much of its land by 2050.
Kofe stepped down as a minister in August to successfully campaign for changes to Tuvalu's constitution, which now states it will continue as a country even if its territory disappears because of climate change.
He said in an interview a treaty signed by Tuvalu with Australia last month, to allow citizens to migrate against the backdrop of climate change, encroaches on Tuvalu's sovereignty and needs to be renegotiated.
"If I am in office, I definitely would approach Australia again to renegotiate the treaty," he told Reuters.
Tuvalu's 16- member parliament is in caretaker mode as campaigning begins for a general election in late January.
There are no political parties, with all candidates running as independents.
Another Tuvalu politician, former prime minister Enele Sopoaga, has also publicly criticised the treaty with Australia, highlighting sensitivity among Pacific islands about preserving sovereignty amid jostling for influence in the region by larger countries including China and the United States.
The treaty commits Australia to defending Tuvalu, which has diplomatic ties with Taiwan, and requires the two countries to mutually agree to Tuvalu forming security arrangements with other foreign partners.
A spokeswoman for Australia's Department of Foreign Affairs and Trade said "the Falepili Union was developed at the government of Tuvalu's request and is focused on Tuvalu's priorities of security, climate change and mobility with dignity".
Kofe, who was not involved in the negotiations, said he welcomed that Australia recognised the threat that climate change posed to Tuvalu, even if the two countries had different views on how to tackle global warming.
"We are also quite happy that Australia is willing to provide a pathway for our citizens to come and live and work," he said.
However the former judge said he was concerned that in seeking to smooth a pathway for 280 people a year to migrate, the treaty allows Australia access to Tuvalu's immigration, customs and citizenship systems.
Kofe said the security clause that requires Australia's agreement on foreign arrangements in matters from maritime to communications also had commercial implications for Tuvalu.
"That takes away our sovereignty, our freedom as an independent nation to make our decisions," he said.
"At the moment we have contracts with a number of companies, international companies that provide satellite connectivity, for example. Do we need Australia's approval now to engage these partners?" he added.
The treaty is not expected to enter into force until after the Tuvalu election.
