Palin appeared alongside Trump at a raucous campaign rally, following days of speculation about the identity of a "special guest."
"Heads are spinnin'. Media heads are spinning! This is going to be so much fun!" Palin yelled from the stage. "Are you ready to make America great again?"
Palin's at times disjointed 20-minute speech was filled with Palinisms like "pussy-footin'," "hallelujah" and "you betcha." With Trump looking on from beside her, she hailed the real estate developer as a "compassionate," "refreshing" and "self-made" man who would bring the country back from President Barack Obama's disastrous tenure.
"Looking around at all of you, you hard working Iowa families, you farm families and teachers and teamsters and cops and cooks, you rock and rollers and holy rollers!" Palin said. "You all make the world go around and now our cause is one."
Palin, who has spoken openly since the 2008 campaign of her anger at the treatment she received from the press and Republican Party leaders, appeared to recognize that Tuesday night marked a moment of comeback.
"I was told, 'You're going to get so clobbered in the press, you are just gonna get beat up, chewed up and spit out.' And I'm thinking -- and?" she said. "Like you guys haven't tried to do that everyday since that night in '08 when I was on stage nominated for VP and I got to say, 'Yeah, I'll go, send me, you betcha, I'll serve!' And like you all, I'm still standin'!"
Trump thanked Palin, calling her a "special" and "amazing" person.
"This is a woman that, from Day 1, I said, 'If I ever do this, I have to get her support,' " Trump said.
Palin's surprise appearance added an extra dose of energy to the crowd, many of whom waited hours outside in the snow to see Trump in person.
Jim Handsaker, a farmer from Story City, Iowa, said Trump should choose Palin as his running mate. He complained that the former governor was ill-served by McCain and his campaign.
"We liked her last time. The problem McCain had is that he didn't unleash her, let her do her thing. I think that hurt him bad," Handsaker, said. "I'd like to see her as vice president. Wouldn't you?"
Chris, a 53-year-old banker from Boone, Iowa, who declined to share her last name, said Palin's endorsement helps boost Trump's conservative credentials.
"She's a conservative and I like knowing that she's speaking out on his behalf," she said.
Although Palin's national clout has diminished since her last time on the presidential campaign trail, she remains a popular political icon on the right and her support marks a significant seal of approval as Trump seeks to woo conservative voters. Her backing is particularly meaningful in Iowa, where Palin holds sway with Christian conservatives -- a group Trump is competing for votes against Texas Sen. Ted Cruz ahead of the February 1 caucus.
Palin's endorsement does not come as a total surprise. Trump's political director, Michael Glassner, was a senior aide to Palin in the 2008 campaign. And Palin and Trump have previously exchanged public praise
Trump said over the summer that he would "love" to have Palin serve in as a Cabinet member in his administration.
"She really is somebody who knows what's happening and she's a special person," Trump had said. "She's really a special person and I think people know that."
But there had also been speculation that Palin may endorse Cruz, whom she has also spoken highly of and endorsed in his 2012 Senate bid.
In an interview with CNN's Jake Tapper
last month, the ex-governor said her two favorite candidates in the 2016 race were Trump and Cruz.
Tony Perkins, head of the Family Research Council, said Tuesday that it was perhaps "natural" to see Palin throw her support behind a candidate who -- previous to this White House bid -- was best known for being a reality TV host.
"For a lot of reasons, intentional or not, she has become more of a celebrity than a political leader," Perkins said of Palin.
But he also acknowledged that in a race that has become so competitive, every endorsement matters.
The Trump campaign "is playing very serious ball here in Iowa and if this were isolated and one endorsement, that's one thing," Perkins said. "But if you're beginning to see a series of endorsements of people who have notoriety in the political world ... it's a factor."
If there was palpable excitement about Palin's endorsement among Trump fans on Tuesday, the news could irk some leaders on the right who do not view Trump as conservative enough on social issues like women's reproductive issues.
Marjorie Dannenfelser, president of Susan B. Anthony List, told CNN on Tuesday that she had concerns about Trump floating former Massachusetts Sen. Scott Brown as a potential vice presidential pick.
"I would ask Sarah Palin to take a look at who Trump has said he might have as his VP. Scott Brown is absolutely unacceptable to the pro-life movement and should be unacceptable to her," Dannenfelser said. "She should not endorse a candidate that would entertain a pro-choice vice president. That's my view."