Latham, who is running as an upper house candidate, will also lead the minor party in NSW.
The former federal Labor leader 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’s 2GB radio today.
“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.”
But his former Labor colleague Chris Bowen said it was unlikely Latham would be able to maintain a working relationship with Hanson through to the March election.
“They have fallen out with everybody they ever worked with, how long do you give this marriage? Not very long, I suggest,” Bowen told reporters in Sydney.
He labelled Latham a “sad and pathetic joke”.
“Pauline Hanson and Mark Latham deserve each other.”
Prime Minister Scott Morrison likened Latham to reality TV show The Bachelor, given his political promiscuity.
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.
“He’s been handing out roses to the Labor Party, to the Liberal Democrats and now he’s handing out one to One Nation,” Morrison told reporters.
“Who knows who he’ll go home with?”
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,” 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.”
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.
Upon hearing the news, former Tasmanian Labor premier David Bartlett called him a “sick, sad, sorry loser”.
Latham led Labor to defeat against John Howard in 2004 before quitting federal parliament in 2005.
NSW Labor leader Luke Foley said his party wouldn’t be doing preference deals with One Nation.
“I challenge the Liberals & the Nationals to make the same commitment,” Foley tweeted.
Latham in recent years has lost jobs with Sky News and the Australian Financial Review for making offensive comments.
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