Palin brought her folksy style to the stage, saying that Trump would "kick ISIS' a**" and saying that America should stop "pussy-footing around," eliciting cheers from the audience.
"When I heard she was going to endorse me I was so honored, you have no idea. I was so honored,” Trump said at his rally in Ames, Iowa.
Palin gave a ringing endorsement to the real estate mogul.
"He's perfectly positioned to let you make America great again. Are you ready for that, Iowa?” said Palin. “No more pussy-footing around.”
Palin spoke for nearly 20 minutes.
She hailed the fact that Trump’s experience was in the private sector rather than as a politician in Washington DC, and said she strongly believes Trump would be a commander in chief who will “kick ISIS’ a**.”
Palin will travel with Trump to two events tomorrow in Norwalk, Iowa and Tulsa, Oklahoma.
Monday night, Trump said he had a "big announcement" and that he would joined by a "very special guest,” but that was kept under wraps.
Palin's backing has the potential to be a big boost to Trump’s campaign in Iowa with its conservative electorate and critical evangelical Christian voting bloc. Texas Sen. Ted Cruz has been leading Trump in recent polls in the state.
Earlier, Cruz tweeted: “Regardless of what she does in 2016, I will always be a big fan,” of Palin.
Palin, the 2008 GOP vice presidential nominee, has long praised Trump.
In a Fox News interview last August, Palin commended Trump's immigration policy as "common sense” and, in a Facebook post in December, she praised Trump's proposed ban on Muslims entering the U.S.
Last year, in a Palin went so far as to call Trump a "hero."
"Trump is the candidate giving voice to untold millions of fed-up Americans witnessing a purposeful destruction of our economy and the equal opportunity for success that made America exceptional," she wrote on Facebook.
For his part, Trump has said he would “love” to have Palin in his administration. Palin told CNN she would love to be Trump's energy secretary. In 2011 the two appeared together at a New York City pizzeria when there was speculation Palin, herself, would run for president. At the time, Trump called Palin a “great woman” and a “good friend.”
And there are other connections too: Palin's former chief of staff, Michael Glassner, is currently Trump's national political director.