“I’m proud to endorse Donald J. Trump for president,” Palin said in a statement provided to The New York Times.
Palin is scheduled to appear with Trump Tuesday evening at a rally at Iowa State University.
Trump said in a statement he is "greatly honored" to receive Palin's endorsement.
Earlier in the day the billionaire real estate mogul set off a flurry of speculation after posting a teaser online for a "very special guest" joining him at his Iowa State University rally.
Palin's endorsement comes as recent polls put Trump and Sen. Ted Cruz (R-TX) in a dead heat in Iowa, a testing ground for the still-crowded Republican primary field.