Palin, the former Alaska governor who was McCain's vice presidential running mate last year, will campaign for McCain's re-election bid as a senator from Arizona, the senator said in a statement on Wednesday.
Palin will be in Phoenix for events on March 26 and 27.
There has been plenty of sniping between the Palin and McCain camps after they lost the election to Democrat Barack Obama but McCain and Palin themselves have remained on friendly terms.
"I'm looking forward to getting back on the campaign trail with my former running mate, and I know my fellow Arizonans will welcome her as well," McCain said. "Sarah energized our nation and remains a leading voice in the Republican Party."
Palin said on her Facebook page that she will also be campaigning for Texas Governor Rick Perry, a Republican, and Minnesota Republican Michele Bachmann.
"We are already making plans to support the candidates our nation needs to make a difference and speak for everyday Americans," she said.
McCain has no announced challenger yet for the Republican nomination but conservative radio talk show host J.D. Hayworth has talked of possibly challenging the Vietnam war hero.
Palin is now a star of the Republican Party and a big draw on the fund-raising circuit. She is a Fox News contributor.
Her best-selling memoir, "Going Rogue," talked of her Alaska upbringing and her frustrations with McCain's top aides, who have denied her charges.