The Senate has approved Labor's amendments on medical transfers after securing the support of Senator Derryn Hinch.
Key crossbench senator Derryn Hinch has backed a contentious medevac bill to make it easier for asylum seekers to get medical treatment in Australia.
The bill passed the Senate on Wednesday 36 votes to 34, after Justice Party Senator Derryn Hinch confirmed his support for the bill.
Senator Hinch, who supported the changes late last year, had second thoughts, but a security briefing Wednesday morning appears to have satisfied his key concerns.
"I think it's the right decision, it's a humanitarian decision," Senator Hinch said.
"It has been a very tortured 24 hours, there has been a lot of pressure from a lot of people on all sides of the chamber."
The amended legislation allows two doctors to recommend the critically-ill asylum seekers to be transferred to Australia.
Labor's amendments extended the home affairs minister's veto powers to block medical transfers on security risks or if they have serious criminal records, and extended the time ministers have to make a decision to 72 hours.
But, crucially for Senator Hinch, the new rules only apply to those already on Manus Island and Nauru.
"It stops there. It's not an encouragement, I believe, to boat people or to people smugglers, who are despicable and should be despised, because it will only apply to people who are there."
Labor successfully moved to bring on debate on the contentious bill in the Senate, after they combined with the crossbench in the lower house to defeat the government on the legislation on Tuesday.
In a fiery start to the debate, Leader of the Opposition in the Senate Penny Wong said the government had demonstrated "a pattern of deceit", saying it had resorted to "smear and fear".
"They are led by a desperate Prime Minister who is leading a bitterly divided government. He is clearly only concerned about one thing, clinging on to his job. This is the only thing that this has always been about," Senator Wong told the chamber.
"Why don't you just call an election?"
Senate Government Leader Mathias Cormann hit back, saying people who have been convicted of low level offences or accused of serious crimes will be allowed to come to Australia on doctors say so.
"As a result of Bill Shorten's bill, rapists, murderers and paedophiles will still get a free pass into this country," Senator Cormann said. "Bill Shorten should be ashamed himself."