Mr Christensen, who was the MP for the Queensland seat of Dawson, says he is going to be announced as a candidate for Pauline Hanson's party ahead of the May 21 federal election.
The controversial MP had retired from politics ahead of the 2022 poll.
Earlier this month he quit the LNP, citing his disenchantment with the party's direction, its net-zero climate pledge and "destructive pandemic policies".
"I have joined Pauline Hanson's One Nation," he said in a video posted online on Wednesday, adding he was approached by the party late last year and is now a paid-up member.
"Today One Nation is going to be announcing me as a candidate."
LNP Senator Matt Canavan said while he understood Mr Christensen might have been upset with some party room decisions, change had to be fought for.
"It is a desertion," he told Nine Network.
"You don't go off and speak to a minor party."
It is not clear if Mr Christensen plans to run for his old seat of Dawson, which he held with a margin of 14.6 per cent, or stand for a Senate spot.
One Nation has already announced small business owner Julie Hall as its candidate for Dawson.
Asked if Mr Christensen could threaten his Queensland Senate seat if he ran for the upper house, Senator Canavan said he took nothing for granted.
"Ultimately you don't have job security ... It's up to the voters," he said.
"But I love a fight, I don't shirk from a fight."
One Nation on Wednesday said it would field candidates in 151 lower house electorates across the nation.
"It's taken almost 12 months to bed down the team we're taking to voters at this election," Senator Hanson said in a statement.
"It's a significant step up from the 2019 election when we fielded candidates in about a third of Australian electorates."
The party is due to announce its senate ticket for Queensland on Wednesday morning in Brisbane.
One Nation says its membership has grown since the start of the COVID-19 pandemic, which resulted in lockdowns at various times in major cities across Australia.
Queensland Acting Premier Steven Miles said voters could do better than Mr Christensen, who disagreed with vaccination advice during the coronavirus pandemic.
"Let's not forget how he risked the lives of Queenslanders, undermining their health advice, undermining public safety and public confidence in the vaccination program. All of that was deeply unhelpful," he told reporters on Wednesday.
"One Nation might be the right place for him, but I don't think One Nation has much of a place in Queensland."