After decades of campaigning NSW is on the cusp of becoming the last state in Australia to pass laws allowing people with a terminal illness to voluntarily end their own lives.
It means terminally ill people in NSW will be able to access voluntary assisted dying within 18 months.
The controversial bill passed the upper house with a majority vote of 23 to 15 just after midday on Thursday, after a marathon 12-hour debate the previous night.
It will now return to the lower house and then go back to the upper house for final approval. That's likely to happen later on Thursday.
The bill was introduced into the lower house in October by Independent MP for Sydney Alex Greenwich, with coalition and Labor MPs allowed a conscience vote on the issue.
The bill allows adults with a terminal diagnosis and up to six months to live to voluntarily end their lives with assistance with the approval of two independent doctors.
Debate stretched passed the parliament's cap at midnight, with MLCs considering close to 100 last-minute amendments after resuming just before midday on Wednesday.
The approval of multiple amendments meant the bill had to return to the lower house for a vote.
"Here in NSW it's been a 50-year-long fight to get these laws changed," Steve Offner from Go Gentle Australia told AAP.
"So for many people in the community, it will be an incredible relief.
"To see this bill finally passed, it will be a moment of celebration.
"It would also be a bittersweet moment for many people, given that there are so many people that in this law has just come too late."
Labor MLC Greg Donnelly had proposed more than 30 amendments, including that terminally ill patients with mental illnesses including bipolar disorder or depression not be able to access voluntary assisted dying.
He also proposed that patients be capable of clear, unambiguous communication.
Supporters of the bill said changes to definitions around communication risked making euthanasia inaccessible for patients with motor neurone disease, or locked-in syndrome.
Mr Donnelly also proposed that religious aged care facilities be able to block residents from access to voluntary assisted dying.
The majority of his amendments were defeated in divisions.
Amendments that would have allowed data monitoring of assisted dying by Independent MP the Rev Fred Nile were rejected, however further data collection amendments introduced by Labor MP Adam Searle were later accepted.
"I am pleased that some degree of data collection has now been amended into the bill," Mr Nile told AAP.
"However, in time the application of this deadly bill will show the need for further scrutiny and oversight which is what my amendment intended."
Amendments from Mr Donnelly, Labor MP Adam Searle and Education Minister Sarah Mitchell were approved.
