This story has been updated.

Sen. Marco Rubio (R-Fla.), the son of Cuban immigrants who made a remarkably rapid ascent through Florida politics, announced that he is running for president Monday afternoon, in front of supporters in Miami.

"Tonight, grounded by the lessons of our history, but inspired by the promise of our future, I announce my candidacy for president of the United States," Rubio said, in front of a banner with the slogan "A New American Century."

"I know my candidacy might seem improbable to some watching from abroad. After all, in many countries, the highest office in the land is reserved for the rich and the powerful," Rubio continued, to cheers and chants of "Marco! Marco!" "But I live in an exceptional country...I live in an exceptional country where the son of a bartender and a maid can have the same dreams and the same future as those who come from power and privilege.

Rubio, 43, first told supporters the news earlier Monday, during a conference call. He joins a pair of other Senate freshmen--Rand Paul (R-Ky.) and Ted Cruz (R-Tex.).--as the first major candidates to announce their bids for the GOP nomination in 2016.

Rubio made the announcement in Miami, his hometown, in front of the city’s Freedom Tower--an iconic, Ellis Island-like landmark where the federal government once processed Cuban immigrants fleeing the Castro regime. The downtown site holds great personal importance for Rubio, his family and the city's influential  Cuban-American community.

"A collection of immigrants and exiles, of former slaves and refugees, together built the free-est and most prosperous nation ever," Rubio said.

Aides said early Monday that 3,512 people requested tickets before registration for the event closed on Friday. Requests for tickets came from every state except Vermont. The tower can only hold about 1,000 people, so a spillover site will be established across the street near the American Airlines Arena, where the Miami Heat basketball team is scheduled to play the Orlando Magic after Rubio's kickoff. A jumbotron screen there allowed the crowd to watch the event.

Monday's dramatic announcement seemed likely to launch Rubio near the top of a crowded field of GOP presidential candidates even as recent polls have suggested that he will have to compete for support among other frontrunners, including former Florida Gov. Jeb Bush, who was a close ally of Rubio's during his rise to power.

Rubio's speech included implicit -- but obvious -- contrasts with both Bush and the Democratic frontrunner, former Secretary of State Hillary Rodham Clinton. In his remarks, without naming Clinton, Rubio referred to her only as "a leader from yesterday."

"Yesterday is over. And we are never going back," Rubio said, as the crowd cheered. "Before us now is the opportunity to author the greatest chapter yet in the amazing story of America. We can’t do that by going back to the leaders and ideas of the past."

In recent weeks, Rubio has done little overt campaigning and has avoided joining the early fray, focusing instead on holding a handful of discreet fundraisers in New York, California, Texas, Illinois and Washington while consulting his family and close circle of advisers ahead of a formal launch.

But soon, he is expected to launch a tour of early primary states. After his announcement on Monday, he'll return to Capitol Hill on Tuesday. On Thursday he'll travel to Boston for a fundraiser, before traveling to New Hampshire on Friday to join other GOP presidential candidates at a Republican summit, in Nashua, N.H.

Rubio is one of four Republican senators expected to run for president. Cruz launched his campaign last month; Paul jumped in last week. Sen. Lindsey O. Graham (R-S.C.) has already established a formal exploratory committee and is hiring staffers in early primary states.

Like Cruz and Paul, Rubio is a younger first-term senator who won his seat with the help of grassroots, tea party-inspired support. With Cruz and Rubio in the race, Republicans will have their choice of two Cuban-Americans whose parents fled the oppressive Castro regime running for president.

While Cruz and Paul have cast themselves as renegade Republicans willing to openly feud with top GOP congressional leaders, Rubio has taken a hybrid approach. He has surrounded himself with a team of political and policy aides who have worked for Republican presidents or top-tier presidential campaigns and has spent the past year restoring his conservative credentials by embracing tea party-inspired anger and concern for the growing size of government and President Obama’s foreign policy.

Ahead of his expected announcement of a presidential campaign on Monday, Sen. Marco Rubio (R-Fla.) released this video of oratory highlights. (Marco Rubio via YouTube)

Rubio’s road to the White House faces several hurdles, including his youth and inexperience on the national political stage and his previous work to broker an ambitious bipartisan immigration reform plan.

Already Rubio’s campaign has drawn comparisons to Obama’s 2008 bid when he was also a first-term forty-something senator with less than four years of Senate experience. The decision of Obama's 2008 primary season rival, former secretary of state Hillary Rodham Clinton, to launch her own campaign the day before Rubio's set up the possibility of a similar contrast seven years later.

Rubio's team has embraced the generational contrast with Clinton and dismissed concerns about his perceived youth or inexperience. He recently defended his record in a Fox News interview, saying that Obama "was a back bencher in the state legislature in Illinois and I was in leadership all nine years that I served there including two as Speaker of the House."

Rubio also enters the race with a clear financial disadvantage. Bush, one of his original political sponsors and mentors, has been traveling the country collecting tens of millions of dollars from top-dollar donors in anticipation of his own campaign.

Rubio hopes to raise at least $50 million by the time the early primaries begin next year, according to associates. Last week some supporters also launched a super PAC, called Conservative Solutions, to back his campaign. Rubio also enjoys his own national donor network that he first cultivated during his upstart 2010 Senate campaign. The network includes several wealthy backers, including veteran GOP financier Wayne Berman; George Seay, a Dallas-area private equity manager; and Norman Braman, a wealthy Miami-area car dealer who has said he may pledge as much as $10 million to Rubio’s campaign, the new super PAC, or both.

Sen. Marco Rubio, who's running for president in 2016, is known for his stances on immigration and tax reform. Here's the Florida Republican's take on Obamacare, the Islamic State and more, in his own words. (Julie Percha/The Washington Post)

Rubio “represents the future, not the past,” Braman said in a recent interview. “We’re in 2015, it’s not 1988. We have unique problems now and I just believe that Sen. Rubio is the one that can best deal with those problems.”

With Bush preparing to enter the race, it is unclear how two Florida rivals might affect the GOP’s eventual chances of winning the critical swing state in the general election. Many Florida Republicans privately fear that a protracted Bush-Rubio could splinter the party and adversely affect down-ballot races, including the race to succeed Rubio in the Senate. Others believe, however, that only a Florida Republican can help the GOP retake the state after losing it to Obama in 2008 and 2012.

More than any of the major 2016 contenders, Rubio is expected to rely on his emotional personal story to spellbind audiences and build his campaign.

He was born May, 28, 1971 in Miami – meaning he would be the first urban Republican in modern times to become his party’s presidential nominee. During his political rise, he characterized his parents as exiles forced to leave Cuba after Fidel Castro’s communist regime took power. In 2011, Rubio was forced to change his official Senate Web site biography after the St. Petersburg Times and The Washington Post reported that Mario and Oriales Rubio had actually emigrated more than two-and-a-half years before Castro took power. Rubio said he’d mistakenly relied on “family lore,” but his explanation fell flat with some critics who considered it implausible.

Marco Rubio’s rise to prominence

NATIONAL HARBOR, MD- MARCH 5 : Sen. Marco Rubio (FL) speaks at the Conservative Political Action Conference (CPAC) at the Gaylord National Resort & Convention Center on Saturday, March 5, 2016 in National Harbor, MD. (Photos by Amanda Voisard)

His parents struggled to provide for their four children — his father tended bar; his mother worked as a hotel maid and stocked shelves at a department store. In the late 1970s, the family left Miami, looking for better opportunities in Las Vegas.

In Nevada, Rubio and several other family members — who’d practiced Catholicism while living in Florida — converted to Mormonism. The young Rubio, who has had a lifelong fascination with and devotion to religion, was an enthusiastic convert, adopting both spiritual and cultural elements of his new faith. He performed Osmond songs at family get-togethers, mimicking the clean-cut, Mormon stars of the “Donny & Marie Show.”

The family returned to Miami and to the Catholic Church in the mid-1980s, settling in the heavily Cuban-American, inland suburban city of West Miami. Rubio, who still lives in West Miami with his wife, Jeanette, and their four children, now attends both Catholic mass and services at an evangelical Christian church.

Rubio was an indifferent high school student, finishing with a C average; but he was a gung-ho football player, and he earned an athletic scholarship as a defensive back to the small, now-defunct Tarkio College in Missouri. He left after one year, returning to Florida, where he eventually earned a law degree at the University of Miami. Along the way, he incurred large student loan debts, a fact he referenced frequently while arguing for student-loan reform in the U.S. Senate.

At the age of 26, Rubio was elected as a city commissioner in his hometown of West Miami, the first victory in an undefeated streak that includes a 9-year stint in the Florida Legislature and an upset win in the 2010 U.S. Senate race against former Florida Gov. Charlie Crist. In 2007, Rubio became Speaker of the House, the first Cuban-American in Florida history to hold that powerful post, an event of such great moment in the state that a plane had to be chartered to ferry supporters from Miami to the capitol in Tallahassee. At a ceremony celebrating Rubio’s victory, Bush, who was ending two terms as governor, presented him with a sword, dubbing him a “great conservative warrior.”

“I can’t think back on a time when I’ve ever been prouder to be a Republican, Marco,” Bush said.

In office, Rubio clashed with Crist, who had succeeded Bush, over almost everything, including a major initiative to change Florida’s much-maligned property tax structure — a fight that ended with neither man getting what he wanted. The animosity carried over to the 2010 Senate campaign in which the Republican establishment initially embraced Crist, who was a heavy favorite and held a commanding lead in early polls.

Rubio deftly aligned himself with the surging tea party movement, trumpeting a small government philosophy and restrictive immigration measures. Even before the election, he became a national conservative hero, wowing a cheering crowd at the annual Conservative Political Action Conference with an electrifying and deeply personal address.

“I was not born to a wealthy or connected family,” Rubio told an overflow audience, “but I have never felt limited by the circumstances of my birth."

Rubio’s father died two months before the election, and the young candidate moved readers to tears with a poignant open letter. “My dad was the one behind the bar,” Rubio wrote. “My father mattered. He was not famous… but he mattered in a way we too often overlook today. He mattered not because of what he accomplished himself, but because of what his life allowed others to.”

After his decisive victory, Rubio tended to de-emphasize his tea party connections. And he would soon alienate many tea party voters by backing a bi-partisan immigration proposal that included a path to citizenship for undocumented immigrants — which he’d opposed during his Senate campaign. The plan was crafted by four Republicans and four Democrats, known as the “Gang of Eight,” but Rubio became its public face, flooding English- and Spanish-language Sunday talk shows to promote it. He later discarded the idea of a comprehensive immigration bill in favor of an incremental approach conditioned on first tightening border security, but his initial shift to the center on immigration remains a key liability with the GOP’s right wing.

After the damaging immigration debacle, Rubio has fashioned himself as a foreign policy expert, leveraging his position on the Senate Foreign Relations Committee to press a hawkish approach to the conflict in Syria, as well as taking a hardline on Iranian nuclear talks. A recent Senate floor speech critical of Obama’s relationship with Israeli Prime Minister Benjamin Netanyahu was especially heralded by leaders of the conservative movement. He has said that if were elected president he’d revoke any deal the Obama administration cuts with Iran to allow development of that nation’s nuclear energy program.

Rubio has also emerged as one of the fiercest critics of the regimes in Venezuela, where he has accused President Nicolas Maduro of “incompetence” and human-rights violations, and in Cuba. He has accused Obama of “coddling dictators and tyrants.”

In December, Rubio sharply criticized Obama for re-establishing diplomatic relations with Cuba as part of a prisoner swap. When asked by reporters about polls showing young Cuban-Americans want normal relations with the island nations, he answered: “I don’t care if the polls say that 99 percent of people believe we should normalize relations in Cuba… This is my position, and I feel passionately about it.”