"Bienvenidos a todos," the Virginia senator said, a phrase that translates to "welcome to everyone."
Right off the bat, the contrast that the Clinton campaign will seek to highlight between Kaine and the Republican ticket during the general election was clear.
Speaking at Florida International University, a campus that is more than half Hispanic, Kaine described his vision for an inclusive country. Dipping in and out in Spanish several times, he drew on his experiences as mayor, governor and the time he spent helping Jesuit missionaries in Honduras to emphasize the importance of service.
"I've always believed that however you serve, what matters is whether you actually deliver results for people," Kaine said. "That's been my goal in every position I've ever held."
Kaine sheepishly acknowledged that he may not be a household name, saying: "This might be the first time you've heard my name."
But unlike the famous real estate mogul on the other side of the political aisle, Kaine argued, his heart was in the right place.
"Do you want a trash-talking president or a bridge-building president? Donald Trump trash-talks folks with disabilities. Trash-talks Mexican-Americans and Latinos," Kaine said. "With Donald Trump, it's me first!"
Then, riffing with the crowd, he added: "You're right, he doesn't trash-talk everybody -- he likes Vladimir Putin."
Clinton introduced Kaine as someone who has shown a "lifelong commitment to social justice."
"Sen. Tim Kaine is everything Donald Trump and Mike Pence are not," Clinton said. "He is qualified to step into this job and lead on Day 1. And he is a progressive who likes to get things done."
Her introduction of Kaine was in stark contrast to Trump's first event with Pence last weekend. Trump took the stage by himself and spoke at length before turning to the topic of his new running mate. Trump and Pence, who did not know each other prior to this election, also lacked the warmth and admiration that was evident between Clinton and Kaine on stage in Miami on Saturday.
She heralded her pick as a man of faith, willing to work across the aisle and committed to furthering the progressive cause.
"In both of our families, faith wasn't just something we talked about at church on Sundays, it was a call to serve others in every way that we can," she said.
As he looked on from a stool behind Clinton, Kaine lived up to his reputation of "Mr. Nice Guy," grinning and waving to the crowd, and clearly reveling in the moment.
But Clinton warned the crowd: "Make no mistake, behind that smile, Tim also has a backbone of steel."
Pivoting to an issue that holds personal significance for Kaine, Clinton continued: "Just ask the (National Rifle Association). Over and over again he has had the courage to stand up to the gun lobby in their own backyard."
During his tenure as governor, Virginia grappled with the 2007 Virignia Tech massacre
-- the country's biggest mass shooting up until that point. Fellow Virginians to this day praise the way Kaine handled the tragedy -- an episode that they say demonstrated both compassion and governing skills.
Trump offered his thoughts on Kaine via Twitter, saying: "Tim Kaine is, and always has been, owned by the banks. Bernie supporters are outraged, was their last choice. Bernie fought for nothing!"
He later added, "Just saw Crooked Hillary and Tim Kaine together. ISIS and our other enemies are drooling. They don't look presidential to me!"
Friends and colleagues describe Kaine as steady and even-handed, often using the word "decent" to describe his character.
Politically, Democrats expect Kaine could help Clinton rally voters in the important swing state of Virginia, and that his fluency in Spanish will be a big asset as he campaigns in minority-heavy areas of the country.
Rick Ely, a Miami resident attending the event, said he believed Clinton had made a "safe choice."
"I would have preferred to see her choose Elizabeth Warren -- a more progressive agenda that way. But I certainly understand with Virginia being a swing state, the fact that he speaks fluent Spanish, is helpful," said Ely, 58.
Clinton announced her pick Friday night in a message to her supporters, ending weeks of speculation just days ahead of the Democratic National Convention in Philadelphia that's set to kick off on Monday.
But even as Clinton and her campaign methodically vetted a number of potential running mates, it was clear that Kaine was on the fast track.
Both Clinton and her husband, former President Bill Clinton, are personally fond of Kaine and believed he would be a loyal and dependable governing partner.
Aides say as Clinton deliberated over a shortlist of potentials vice presidential nominees, she continued to return to her "unshakable confidence" in his readiness for the job, as well as her personal comfort with him.
During the vetting process, Clinton was advised by her campaign chairman, John Podesta: "It needs to be someone who, whenever they walk into a room, you are glad to see them, and want to have them as part of any conversation."
Ultimately, it was Kaine that best fit that description.
Anita Goldfeld, 76, said she drove from Boca Raton to see Clinton and Kaine's first event together. Goldfeld supported Bernie Sanders during the primaries but is enthusiastically supporting Clinton -- and now Kaine -- in the general election.
"I think that he is a man who knows, who's had a lot of experience, who would be an excellent asset to Hillary," Goldfeld said.
On the criticism that Kaine is a white, male and ashe himself has put it, "boring," Goldfeld responded: "I'll take boring and knowledgeable -- I'll take a decent human being over someone like Donald Trump."