The 28-year-old Salt Lake City native has been the presidential candidate's right-hand man for years, and now as Romney's national finance director, he is heading up the most crucial part of Romney's White House bid.
Zwick, a holdover from Romney's 2002 Winter Olympics, is at the gut of Romney's campaign, and recently oversaw one of the most impressive hauls of campaign cash for a Republican candidate this early in the game: $21 million in less than three months.
Romney and his wife, Ann, have called Zwick their "sixth son," a far cry from when the Brigham Young University student volunteered to translate documents for the Salt Lake Organizing Committee in advance of the Games.
"He's got all the great attributes: he's hard working, really dedicated, and passionate," said Bob White, a former partner in Romney's venture capital firm Bain Capital and a campaign adviser. "The other thing really driving his success: He is a big idea guy."
Zwick's first success in the campaign came a few days after Romney announced his presidential exploratory committee. Zwick organized a large fundraising event and called it a National Call Day. Executives, friends, associates and supporters filled out a convention hall ballroom and raised $6.5 million in one day.
The fundraiser made big headlines, helping to keep Romney in the top tier of Republican contenders even though his name recognition was lacking. Political observers praised the event as a brilliant start of the campaign. Much of the credit was due to Zwick.
Zwick grew up in Utah's capital city and attended East High, but also lived abroad for almost 10 years of his childhood in Chile and Brazil. He served an LDS Church mission to Bangkok, Thailand.
The languages he learned through those experiences landed him a spot translating documents for the Olympic organizing committee and praise from the committee's top guy, Mitt Romney. And Zwick quickly became a fan of Romney.
"When scandal happened morale was pretty low, Mitt came in and was able to energize a community in a way that I don't think anybody's seen," Zwick said.
As Romney headed further into the media and public spotlight, he asked Zwick to serve as his personal aide. Zwick hasn't left his side since.
Zwick joined Romney after the Games when he decided to run for governor of Massachusetts. He helped with the campaign and became deputy chief of staff when Romney was elected, a prominent spot for a 25-year-old.
"They couldn't find anybody else," Zwick joked.
He later left and helped run Romney's political action committee, the Commonwealth PAC, and when Romney formally entered the race, Zwick was still in Romney's close circle of advisers.
"Of all the finance people I've worked with, [Zwick is] the most innovative and creative at thinking of ways to get more people involved in the process," said Kirk Jowers, now chairman of the Commonwealth PAC and also director of the Hinckley Institute of Politics at the University of Utah.
Zwick said the secret to his success was staying close to good people and learning from them. He heralds Romney at every turn, and in an interview had a hard time speaking about himself without interjecting praise of Romney.
"There's a floor mat outside my office that says one word and that's 'passion,'" said Zwick. "That's how I feel about Gov. Romney and people working for him."
Zwick was involved in one campaign bump late last year when the Boston Globe reported that he, as a Romney adviser, participated in efforts to set up a national network of Mormons to boost the governor's bid. Zwick's father, Craig Zwick, is a General Authority in the church's hierarchy.
That was followed by an e-mail from two Brigham Young University professors seeking Romney supporters among alumni of the business school. Zwick, along with church officials denied any concerted effort. The story eventually died and the campaign rebounded quickly.
As for himself, Zwick doesn't want to talk about his plans, though he rules out personally running for office.
"I don't know exactly what I'll do, but at least in the next several years I'm going to do everything I can to get Mitt Romney the resources he needs so he can be the next president of the United States."
He also brushed off a question about whether he had proven himself with the first-quarter fundraising haul. And he doesn't think his age affects his work, for good or ill.
"I don't know the ages of the other folks," he said of his counterparts in other campaigns. "But I think that when you've got a product that sells, age really doesn't matter."
Jack Oliver, who was finance director for President Bush's 2000 campaign and vice chairman of his 2004 re-election bid, said heading up finances for a national campaign required someone with great organizational and management skills and a tremendous work ethic.
"I've been very impressed that a person at such a young age has done such a great job organizing what they've been able to accomplish," said Oliver, who was 30 years old himself in the 2000 race.
Being young isn't a negative at all, Oliver added.
"Age isn't a limiting factor in the business of politics," he said. "It's about whether you handle yourself in a professional manner. The more you are able prove yourself, the more people will give you greater responsibility."
That seems to be the case with Zwick. Age didn't seem to affect Romney's decision to place Zwick in a key role that could make or break his entire White House bid.
Said Kevin Madden, Romney's spokesman, "When you listened to Mozart, you couldn't hear what age he was."
* AGE: 28
* WIFE: Jenny, son Spencer Scott, 2, and another baby boy on the way
* HOMETOWN: Salt Lake City
* ATTENDED: East High School, Brigham Young University
* CURRENT TITLE: National finance director, Mitt Romney campaign
* FORMER POSITIONS: Special assistant to Romney during the 2002 Winter Olympics, former deputy chief of staff to then Massachusetts Gov. Romney