Former Labor leader Mark Latham is joining forces with Pauline Hanson as a One Nation candidate for the upper house of the NSW parliament.
Mr Latham, who will also lead the minor party in NSW, said the stakes were "too high" for him to sit on the political sidelines any longer.
"This is a fight for our civilisational values. For free speech, for merit selection, resilience, love of country," he told Sydney radio station 2GB on Wednesday morning.
"All of them under siege from the left, and a lot of it is happening in state politics as much as federal.
"I'm in a position and a stage in life where I just can't stand on the sideline talking about it, I want to get stuck in and play a role as a legislator."
Mr Latham plans to campaign on issues of immigration, congestion and over- development in Sydney.
He also counts failings in the education system, political correctness, identity politics and power prices among his most pressing priorities.
"One Nation has the policies and NSW certainly needs a third choice - Labor and Liberal are on the nose," Mr Latham said.
"I want to provide people with a choice, a third choice, to say you can vote One Nation and have practical, common sense solutions to these big issues in our state."
Senator Hanson said her new recruit would help put the major parties on notice.
"I intend to take it up to them in the federal (parliament) and Mark will take it up to them in the state and let's get this country moving," she told 2GB.
"These major political parties here won't have their own way. We need policies that are driven with ideas and driven by good policies, and to get the state moving."
Upon hearing the news, former Tasmanian Labor premier David Bartlett called him a "sick, sad, sorry loser".
The one-time Labor leader did ads for both One Nation and the Liberal Democrats during this year's Longman federal by-election, earning him the title of "king rat" from his former party colleagues.
Mr Latham led Labor to defeat against John Howard in 2004 before quitting federal parliament in 2005.
He says he was sacked as a columnist for Australian Financial Review in 2015 for making offensive comments about domestic violence campaigner Rosie Batty.
Mr Latham was also turfed from a co-hosting role on Sky News for making offensive remarks.