NSW Greens MLC John Kaye is being remembered as a fearless, principled and formidable politician, following his death from cancer at the age of 60.
Tributes are flooding in for the upper house MP who passed away surrounded by family and friends at his Sydney home on Monday night.
Dr Kaye was diagnosed with the aggressive disease in February and was undergoing treatment.
NSW MP Jamie Parker described his Greens colleague as a respected party elder and enormous contributor to public debate.
"We've lost a brave, tireless activist and a wise, fearless mind," Mr Parker told parliament on Tuesday.
"We've lost a comrade, a colleague, a friend.
"Our community and this world has lost a champion for renewable energy, for public education, and one of the greatest advocates against the agenda of privatisation and sell-offs."
Premier Mike Baird said Dr Kaye, who was elected to parliament in March 2007, was a great warrior who went into battle with grace, dignity and passion.
"This is not about political badges, it is about a friend and colleague in the pursuit of fighting for the community that we all love so much," Mr Baird said.
"He certainly was a political opponent, but I count him very much as a friend and someone who I admired immensely."
NSW Labor Leader Luke Foley meanwhile remembered Dr Kaye as one of the state's most effective politicians in the past 10 years.
"He made his presence felt; his profile in the state's political and parliamentary debates I think belied his official role as an upper house member from a minor party," Mr Foley said.
"He made an impact by dint of great intellect and sheer relentless energy."
Australian Greens Leader Richard Di Natale said Dr Kaye's death is being felt across the country.
"We will all miss his energy, passion and commitment to social justice and sustainability," Senator Di Natale said.
"Our hearts go out to his partner, Lynne, and his family at this time of deep loss."
The tributes also poured in on social media.
"Sorry to learn of the death of (John Kaye)" tweeted former NSW Premier Barry O'Farrell.
"Despite many political battles I always enjoyed our chats on level 2."
Before entering parliament, Dr Kaye taught and researched electrical engineering at the University of NSW where he specialised in sustainable energy and greenhouse issues.
He obtained his PhD from the University of California Berkeley.
The Legislative Council was adjourned on Tuesday as a mark of respect to Dr Kaye.
A private funeral service will be held in Sydney this week.