Lake's campaign said Gabbard would introduce Lake at a GOP forum in Chandler.
Gabbard tweeted out a statement early Tuesday saying she looked forward to supporting Lake, who she said "isn’t afraid to call out the elite cabal of permanent Washington and the military industrial complex and their propagandists in the mainstream media."
“For too long, establishment leaders from both parties have sought to enrich themselves, play games, and build up their power while ignoring and even enabling the suffering of millions of hard-working Americans," she said. "Kari Lake is a leader who puts people first, fighting for border security, energy independence, public safety, and other policies that actually make life better and more affordable for the American people.
The dramatic swing to the right comes after Gabbard, a former House member from Hawaii who ran for president as a Democrat in the 2020 election cycle, posted a video statement saying she could no longer remain a member of a party “now under the complete control of an elitist cabal of warmongers driven by cowardly wokeness.”
Gabbard has often been at odds with Democratic leaders, despite having endorsed Joe Biden in the 2020 race after she dropped out. But she will now campaign for a Trump-endorsed candidate who has become a prominent election denier in Arizona.
NBC News has asked Gabbard for comment.
Lake repeatedly declined to say in an interview Sunday on CNN’s “State of the Union” whether she would accept the results of the election next month if she loses to Democrat Katie Hobbs. She had remarked earlier that midterm elections could be tainted by fraud.
Others speaking at Tuesday's GOP forum include Senate candidate Blake Masters and Abe Hamadeh, who is running for attorney general. All three of the candidates scheduled to take the stage Tuesday have denied the results of the 2020 election.
Last week, GOP Gov. Doug Ducey and former Vice President Mike Pence, who both rebuffed former President Donald Trump's pressure to overturn the 2020 election results, backed Lake and Masters. Ducey, who chairs the Republican Governors Association, had endorsed Karrin Taylor Robson over Trump's pick in the GOP primary.