Outgoing Liberal senator Nick Minchin says his role in defeating the 1999 referendum on Australia becoming a republic was the "greatest pleasure" of his career.
Watched by his wife Kerry and their children Jack, Oliver and Anna, the former minister used his valedictory speech to reflect on 18 years as a member of the upper house before his term in the red chamber ends on June 30.
Senator Minchin spent 16 years on the coalition frontbench, including nine years as a cabinet minister under former prime minister John Howard.
"I remain surprised by the opportunities I have had, none of which I expected," he told the Senate on Tuesday.
Senator Minchin said conservative issues that were raised during his time in parliament, such as the monarchy, would keep his interest after politics.
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"Nothing in my long career in campaigning has given me greater pleasure than the comprehensive rejection of that republican model," he said.
"One cause I will remain actively involved in after I leave this place is the advocacy of our current constitutional arrangements."
Regrets, the senator had a few.
"I failed to have the courage of my conservative convictions concerning my serious reservations at the time about the US plans for the invasion of Iraq," he said.
The introduction of Work Choices by the Howard government in 2005, which contributed to its defeat two years later, was a lesson Senator Minchin hoped the coalition had learned from.
"The Australian people will only ever accept incrementalism, not radicalism, when it comes to industrial relations reform," he said.
"And I regret my incapacity to create the circumstances in which John Howard may have seen the wisdom of retiring on the 10th anniversary of his prime ministership."
A battle Senator Minchin never expected to fight upon his entrance to parliament in 1993 was on carbon dioxide.
"Anyone who dares question this as yet unproven theory of anthropogenic global warming is branded a denier," he said.
"Thus upon leaving the parliament, I am contemplating the foundation of an organisation called the Friends of Carbon Dioxide."
The senator was instrumental in installing Tony Abbott as leader of the Liberal Party at the end of 2009, in opposition to the proposed emissions trading scheme agreed to by then leader Malcolm Turnbull.
Senator Minchin expressed his gratitude to the upper house for its support after his son was badly injured while training as an officer cadet at the Australian Defence Force Academy in February last year.
