Remember: A little-known senator from Illinois did just that at the 2004 Democratic convention, and he's now running for reelection as president of the United States.
Of course, Christie ostensibly won't be promoting himself. He has been chosen as the best pitchman to those independent and centrist Americans who have yet to settle on either the incumbents, President Obama and Vice President Biden, or the challengers, Romney and U.S. Rep. Paul Ryan.
Why Christie? Because he is "a leader of the effort to reform government, and to control spending at the state level," Eric Fehrnstrom, a senior adviser to Romney, said Tuesday in an interview during a Romney campaign stop in Zanesville, Ohio. "His election in 2009 electrified [Republicans] across the country, that he won a deeply blue state. We need more people like Gov. Chris Christie."
The governor's relationship with Romney was a key to the decision to give him what arguably is the most important speaking role at the convention. Romney "admires him for his strong fiscal management, and as a friend," Fehrnstrom said.
Christie issued a statement Tuesday through the Republican National Committee that said in part: "The challenges we face as a country are great and require the honesty and boldness of the Romney-Ryan team. We have an opportunity in Tampa to make clear that if we tell each other the hard truths, tackle the big problems, and make bold choices, we will see America's comeback."
Note the comeback word. That's the word Christie has been using in New Jersey to sell his fiscal policies to hometown voters, and it's now being used on the Romney campaign trail. Because of the "New Jersey comeback" that Christie ushered in, the governor argues, New Jersey is ready for a tax cut.
New Jersey Democrats say the state is still broke, with unemployment higher than the national average, and can't afford a tax break.
"While Chris Christie throws out his 'Jersey Comeback' slogan around the nation campaigning for Mitt Romney, the folks back home in New Jersey are really feeling a 'Jersey Setback,' " Assemblyman Louis Greenwald (D., Camden) said in a statement after Tuesday's announcement.
Christie will have a huge stage to offer a rosier view of the Garden State on Aug. 27, but pollster Patrick Murray of Monmouth University said he needs to be careful not to talk too much about himself.
"You can't be seen as blatantly tooting your own horn when you're up there," Murray said. Christie's experience in New Jersey, he said, should be secondary.
Murray speculated that the speech could shape up like this: "It's Republican ideas that spark change . . . when we put our best ideas forward, Democrats have to get in line, as my experience in New Jersey shows."
One of Christie's closest political advisers, Bill Palatucci, said the governor was writing the speech himself - he's on the fourth or fifth draft.
Palatucci said he didn't know the specifics but imagined that the speech might resemble what he heard last week when Christie, stumping for Romney out west, spoke of the need for "strong leadership" in the nation.
"I'm sure he'll have a couple of surprises for us, but I don't think it's much more complicated than that," Palatucci said.
He noted that at a recent GOP governors' event in Colorado, Romney called on Christie to speak last.
"The governor, as usual, knocked it out of the park," Palatucci said. "I don't know if that was the deciding factor, but I just know I've been present when the governor's been on his game in front of Mitt Romney. . . . Romney's seen him in action, and figured: 'That's the guy I want.' "
Though Christie is better known for his biting, funny, back-and-forth exchanges with constituents and reporters than his rhetoric in big speeches - and though the huge audience may make him nervous - Murray says Christie will do well.
"You give Chris Christie prime-time television, and he's going to run with it," Murray said. "He's going to come off as personable, he's going to come off as down-to-earth, he's going to come off as someone that you can relate to."
And for Christie, being keynoter may be easier than being running mate - "because now he still gets to be Chris Christie," Murray said. "Rather than be tied down to anything negative that might happen in the campaign, he can distance himself from specifics of Mitt Romney while still doing the fund-raising circuit and rallying the troops."
The big speech also sets him up for the future: Either U.S. attorney general if Romney wins, or 2016 candidate if Romney loses.
A Romney loss might bode ill for the tea party, which is aligned with Ryan, or signal the need for "someone to do well with moderate voters in northeastern blue states."
"And who else could that be?" Murray asked.
Christie wasn't talking to local reporters about his selection Tuesday, and he has not done a news conference since it was reported that he was among five finalists to be Romney's running mate.
His office said he was vacationing with family at the Shore. But he told USAToday on Monday that in his speech he would "try to tell some very direct and hard truths to people in the country about the trouble that we're in and the fact that fixing those problems is not going to be easy for any of them."
If that sounds dour, he also said his address would touch on his successes dealing with these issues in New Jersey.
He is no stranger to national speeches, in which he often pivots from his successes in New Jersey to Obama's alleged failures. While he has had success dealing with a Democratic legislature, he says, the Democratic president has looked lost dealing with the GOP on Capitol Hill.
Of late, Romney has noted the need for bipartisanship, a theme Christie has invoked. "In New Jersey, we've . . . put our state's interests ahead of partisan interests," he told a black-tie dinner at the libertarian Cato Institute in May. "And we have made friends with our Democratic colleagues who are willing to view these things not in a partisan way, but in a commonsense way."
He could mention his landmark public-benefits bill, passed in 2011 over fierce objections from unions, and pivot to Romney and Ryan's calls for confronting entitlement costs. He often refers to entitlement reform as one of "the big things."
"Leadership, today in America, has to be about doing the big things and being courageous," Christie told an American Enterprise Institute audience last year.
Or he could invoke a theme that drew big applause at the Reagan Library in California a year ago - "American exceptionalism." Romney uses that one, too.
"If we are to reach real American exceptionalism - American exceptionalism that can set an example for freedom around the world - we must lead with purpose and unity," Christie said before attacking Obama for wanting to "divide" America.
Regardless of the keynote speech's contents, its announcement is building the speaker's profile. Palatucci said the Christie camp was "flooded" Tuesday with requests from state GOP delegations for Christie to meet with them during the four-day convention.
Christie was the first governor and one of the most prominent Republicans to endorse Romney for president in October. That endeared him to the Romney camp and certainly helped him land on the short list for running mates. Also on that list was a GOP star, Sen. Marco Rubio of Florida, who will introduce Romney to the Tampa audience.
He won't be the first New Jerseyan to keynote a convention. Gov. Tom Kean Sr. did so in 1988 when President George H.W. Bush was nominated. In 1992, then-Sen. Bill Bradley headlined Bill Clinton's Democratic convention.
Often, the keynoter benefits most from the speech - if he delivers the goods. Then-New York Gov. Mario Cuomo's stirring 1984 address had Democrats salivating for him to run for president. The message of the 2004 keynote that launched Obama: Forget the red-blue divide, we are one America, with shared values. "I'm LeBron, baby," Obama reportedly said after rehearsing.
But even a crappy speech isn't fatal. The Arkansas governor who delivered the Democrats' 1988 keynote droned on so long that people began talking in the hall and drifting out. When Bill Clinton said, "In conclusion," conventioneers erupted in a sarcastic cheer. Four years later he was elected president.
Asked if he sees his speech as a springboard for a future presidential bid, Christie told USAToday on Monday: "It's not what you say but what you accomplish."
But it's also how viewers feel at home.
"How much of Barack Obama's  speech do we remember?" asked Murray, the pollster. "It was the sense, the excitement that he generated by giving the speech. That's what we remember. And that's what Chris Christie's job is to do."
Contact Matt Katz at 609-217-8355 or firstname.lastname@example.org, or follow on Twitter @mattkatz00. Read his blog, "Christie Chronicles," at www.philly.com/ChristieChronicles.