Correction: This article incorrectly identified Jonathan Skrmetti as an assistant district attorney. Skrmetti is an assistant U.S. attorney. Additionally, when Katie Biber’s sisters were born, her family was not yet living in Lee’s Summit as previously noted. This version has been corrected.

Katie Biber Chen, a lawyer overseeing Mitt Romney's ballot registration and delegate selection. (Courtesy of Mitt Romney for President)

Last fall, Katie Biber, the Romney campaign’s general counsel, gave her visiting parents a tour of the candidate’s Boston headquarters. To her mother, she explained a board in her office listing delegate counts, saying she hoped it would pay off “in the long run.” Near her father, she barked orders to staffers about the number of signatures needed to get on the ballot in Virginia: “If we have to have 100, I want 200!”

“And that’s how she does things,” said her mother, Mary Biber. “She’s organized. That’s how she planned her wedding. We all called her the wedding Nazi.”

If Mitt Romney manages to capture the Republican nomination, it probably won’t be because of his dynamite personality or the magnetism of his message. Instead, he will owe his victory to a superior campaign organization personified by the obsessive plodding of his diminutive delegate counter.

In the Boston headquarters, a few blocks from the North End apartment Biber, 33, shares with her husband and two young sons, she can be seen hugging black binders full of delegate information, wearing a Romney sweatshirt with the words “Legal team” stitched on the arm, or walking reporters through the campaign’s operations in major states such as Illinois, where Romney added to his delegate advantage Tuesday.

To some in the outside world, Biber is most recognizable as the legalistic voice of certain doom, quantifying the implausibility of a Rick Santorum or Newt Gingrich nomination.

“It’s becoming increasingly mathematically impossible for Rick Santorum to get to the 1,144 delegates necessary to win, and they know that,” Biber said in an interview Tuesday. “That’s why they are starting to talk about things like contested conventions, which they know very well is not the way to win a general election.”

She said Santorum’s only play was to distract from Romney’s delegate advantage with “book-cooking math.”

Biber’s mother said that her daughter — an older sister to attention-grabbing triplets — has always known “what she wanted and how to get it.” Now she wants delegates, and luckily for Romney, she mapped out her strategy early.

Last year, while still at the powerhouse Washington law firm Patton Boggs, she mulled with her legal mentor, Ben Ginsberg, how the forward shift in the primary calendar would upend the nominating process and put more emphasis on delegates.

“Katie knew that was part of her mission,” said Ginsberg, a veteran of many Republican campaigns and a Patton Boggs attorney now serving as the Romney campaign’s national counsel. “And she embraced it.”

Biber has never suffered from lack of determination.

When her parents came home from the hospital with triplet sisters, Katie Biber, not quite 2, asked, “Can’t you take them back?” according to her father, and later declared “I’m here, too!” when passersby showered her sisters with attention. She described home as “chaos,” thanks also to the addition of foreign-exchange students.

From the disorder emerged a highly ordered mind.

Biber became a proficient pianist, favoring Chopin, and played clarinet in the high school band. (Her recent playlist includes Whitney Houston’s “Didn’t We Almost Have It All.”) She gave up music for the debate team, where her parents said she came into her own. When it came time to leave her childhood room (it was so messy, her father said, that police responding to a false alarm about a break-in thought burglars had ransacked her quarters), the family expected her to apply to an affordable state school. Instead, she clandestinely applied to George Washington University, where she volunteered for a local congresswoman and Bob Dole’s ’96 campaign.

“I was basically working full time my last two years of college,” Biber said.

Her break came when a fellow resident of Lee’s Summit, a suburb of Kansas City, Mo., hired her as an intern in the office of then-Sen. Kit Bond (R-Mo.).

“Everywhere I went, I brought her with me,” said David Israelite, the office’s senior staffer who went on to become Biber’s political mentor. (Now the head of the National Music Publishers’ Association, Israelite said he received a call from Biber last month in which she checked on the legality of the campaign’s music. “She’s always making sure,” he said.) For Bond’s reelection, Biber joined the campaign as an opposition researcher, impressing Israelite with her mastery of the opponent’s record and the swiftness with which she produced information for attacks.

Israelite brought Biber with him to the Republican National Committee in 1999 to assist in the presidential election. After the election, she followed Israelite to John Ashcroft’s Justice Department, where she acted as a spokeswoman on issues such as Mitsubishi price fixing, but she wanted something more exciting.

She enrolled at Harvard Law School and immediately made an impact on the Republican scene.

“She clearly wanted to be a significant Republican operator,” said Austin Bramwell, a Harvard Law School classmate who, like Biber, later clerked for Judge Timothy M. Tymkovich in the U.S. Court of Appeals for the 10th Circuit. “Her concern was actual politics — who was promising political horse flesh.”

“I couldn’t get away from the politics,” acknowledged Biber, adding: “Delegates? It was not on my list of hobbies.”

In 2003 she appeared in a Harvard Law Bulletin article called “All the Right’s Moves” beaming behind a Bush-Cheney placard and in front of a cardboard cutout of George W. Bush.

Jonathan Skrmetti, now an assistant U.S. attorney in Tennessee and one of Biber’s roommates in a townhouse off campus, recalled the “incredibly high-energy” Biber snacking on Nutella and participating in the house’s “Buffy the Vampire Slayer” watch parties. She hosted games of Risk but also organized a trip to Washington for conservative students that included personal meetings with Supreme Court Justices Antonin Scalia and Sandra Day O’Connor and then-White House counsel Alberto Gonzales.

In 2004, the year she graduated, she met the Romneys at a small dinner in Boston where the governor impressed her with his grasp of foreign and domestic issues. She kept him in mind as Ginsberg brought her to Patton Boggs in 2006, the year she married Mark Chen, a business executive whom she had met in Cambridge.

They married in Kansas City, which meant that Biber planned the wedding from afar.

“She had a flow chart with us all having assignments,” her mother said. “And she was always checking on me to see if I had done my assignments. And I said, ‘You know, Katie, you can trust me.’ ”

In 2007, she joined the Romney campaign and came aboard again last year. Her husband promotes the candidate and his wife on Facebook, linking to a recent GQ Death Race 2012 power list that placed Biber third in influence that week behind Benjamin Netanyahu and U.N. Ambassador Susan Rice.

Biber said she rejoined Romney because he inspires “fierce loyalty.” People close to her say that she has given her all to putting Romney on a winning track to the nomination.

It is something that her parents hope the candidate appreciates. When Romney was introduced to them at a fundraiser in Missouri, he asked, “‘How much are you guys donating?”

“You know,” Bob Biber recalled answering, “I’ve already donated my firstborn. I’m done.”