Palin will appear with Handel at noon on Aug. 9 in the metro Atlanta area. A precise location has not yet been determined.
In a statement, Palin said she is making the trek to Georgia because "it is absolutely critical that Georgians nominate an ethical leader and a true conservative to take the fight to (Democrat) Roy Barnes in November."
She reiterated that Handel -- who has faced questions about her anti-abortion credentials -- is a "strong, pro-life leader who isn't afraid to take on the status quo and do the right thing."
Palin has said women activists -- or "mama grizzlies" as she calls them -- will lead a conservative wave this November. Palin's support for Nikki Haley in South Carolina is credited with helping fuel Haley's Republican gubernatorial primary win.
Palin's July 12 endorsement of Handel ignited her campaign and provided the former secretary of state with a conservative seal of approval, armor against attacks from fellow Republicans that she's too liberal. Handel catapulted to the top of the seven-person GOP field in the state's July 20 primary. She was the top GOP vote-getter with 34 percent of her party's primary tally.
Handel is locked in an Aug. 10 runoff with Nathan Deal, an ex-congressman from Gainesville, for the GOP party's nomination to take on Barnes in November. Barnes won his party's nomination outright.
The timing of the rally -- the day before the primary -- is designed to whip up the enthusiasm of the Republican base and remind them to get back out to vote, no easy task for a runoff race in the middle of the summer.
It won't be Palin's first trip to Georgia for a runoff. In 2008, fresh off her vice presidential defeat, she swept into the state to headline four rallies for U.S. Sen. Saxby Chambliss as he faced a runoff battle to return to Washington.
That race took on national significance because Chambliss' eventual win over Democrat Jim Martin helped deny Democrats a filibuster-proof majority.
Palin was greeted like a rock star, with huge crowds of supporters lining up in the cold for more than an hour for a chance to see her.
Political experts have said that while Palin's endorsement of Handel was important, her appearance in the state could help seal the deal.
Handel has already been busy touting Palin's support. She's featured prominently in Handel's first television ad of the runoff campaign.
Deal spokesman Brian Robinson said Handel's support is coming from people who don't know her.
"The people who know Karen Handel -- the overwhelming, eye-popping, vast majority of Republican state legislators -- have endorsed Nathan Deal," Robinson said. He touted Deal's endorsement by former U.S. House Speaker Newt Gingrich and Georgia House Speaker David Ralston.