When Patrick Fitzgerald announced at a press conference last May that he was stepping down as Chicago’s U.S. attorney after more than a decade, he looked like a tantalizing catch for any law firm. Fitzgerald was supremely accomplished, respected, and still young at 51. He had made a national name for himself by successfully prosecuting former White House adviser I. Lewis "Scooter" Libby, former Illinois Governor Rod Blagojevich, and former Hollinger International, Inc, chairman Conrad Black.

But at that event, Fitzgerald may have caused a few managing partners’ hearts to skip a beat when—in response to a reporter’s question about his future—he smiled and quipped: "Can you see me as a defense lawyer?"

Five months later—after considering options ranging from starting his own firm to working for a forensic investigations outfit—Fitzgerald joined Skadden, Arps, Slate, Meagher & Flom’s Chicago office in one of the splashiest partner hirings of 2012.

"I had concerns about going to a law firm," Fitzgerald admitted during an interview at Skadden’s Chicago office in December. "It was important to me that I could feel comfortable with who I was representing and enjoy the people I’m working with." To that end, Fitzgerald decided that his long history as a prosecutor would make him uneasy representing the sort of people he used to pursue. So instead of representing individuals, he’s structured a practice focusing on helping companies with internal investigations, working as a corporate monitor, and advising boards of companies facing trouble.

"I have no heartburn about representing companies in trouble where employees have gone off the rails," he explains in his slightly raspy voice. "But I’m not wired to be an individual criminal defense lawyer. I’m not looking to have whiplash." Fitzgerald adds, "If there is an officer who directed a program to pay bribes, that’s not something I feel comfortable with. It’s not a judgmental thing. But I want to be 100 percent on board representing clients."

Fortunately for Fitzgerald, his new firm told him it was fine with this unorthodox decision. "Skadden said: Set out and establish a practice you feel comfortable with," Fitzgerald says. David Zornow, the head of Skadden’s litigation group and a white-collar specialist himself, says he doesn’t expect Fitzgerald’s limits on his practice to be an issue. "I think the feeling is he’s going to be so busy doing the kinds of things he’s interested in focusing on," Zornow says. "We have lots of people, including me, who represent individual defendants." It might be difficult, however, for Skadden to have to explain to the CEO of a longtime client who faces government charges that we’re sorry, but this former U.S. attorney at our firm won’t represent you.

For now, Fitzgerald plans to focus on corporate internal investigations. During the December interview, he said he was already involved in two such matters, which he can’t identify. He’s also lent a hand to a more routine contract dispute. He’s representing Dr. W. Norman Scott, a Manhattan orthopedic surgeon, who’s embroiled in a royalty fight with Zimmer Inc., which makes knee implants, according to court records.

With roughly 170 lawyers in Chicago, Skadden has long had a strong presence in the city, but it was mostly known for its corporate and M&A practice there. Fitzgerald’s hiring boosts its litigation and white-collar profile locally and nationally. "The last time somebody came out [of the U.S. attorney's office] this prominent in Chicago, it might be Dan Webb," says John Cashman of Major, Lindsey & Africa. (Former Chicago U.S. Attorney Webb joined Winston & Strawn in 1985.) "Everybody and their brother contacted us to see if we had a way into him," he adds about Fitzgerald. (Fitzgerald says he got advice from a few recruiters, but didn’t use any to speak to firms on his behalf.)

Fitzgerald’s rise has a near mythic quality. His parents were Irish immigrants who settled in Brooklyn, New York. Fitzgerald’s late father worked as a doorman at an exclusive Manhattan Upper East Side building. As a boy, he attended Our Lady Help of Christians school and played the accordion at Irish social events. He was accepted at Regis High School, a selective Jesuit school in Manhattan that charges working class students no tuition. Amherst College and Harvard Law School followed. After three years as an associate at litigation boutique Christy & Viener, he joined the Manhattan U.S. attorney’s office. In 2001 he was the surprise choice to be U.S. attorney for the Northern District of Illinois, chosen in part because he had no ties to the city. He developed a reputation for being tough, but apolitical. In 2003 George W. Bush’s U.S. Department of Justice tapped him as special counsel to lead the investigation of leaks in the Valerie Plame matter, and he later won the conviction of Libby for perjury and obstruction of justice.

When Washingtonian magazine gave out its best-of-year awards in 2005, Fitzgerald tied with U.S. Supreme Court Justice John Roberts for "Best Performance Without a Script." The publication lauded Fitzgerald for his 66-minute note-free press conference in which he laid out the criminal case against Libby. Fitzgerald also snared another magazine award that year: He was named one of People ‘s sexiest men alive. Fitzgerald didn’t marry until he was 47; he and his wife, a former schoolteacher, have two young children.

"He’s scary smart on the law and has a steel trap mind on the facts," says Fitzgerald’s friend David Kelly, the former Manhattan U.S. attorney who is now a partner at Cahill Gordon & Reindel. Reid Schar of Jenner & Block, an ex–federal prosecutor in Chicago, describes his former boss as "the smartest guy in the room," but someone who listens to others. "He could synthesize a problem and solution more succinctly than anybody," Schar says.

"He was such an attractive candidate that we had been talking about the possibility of trying to attract him to Skadden for a long, long time before he decided to leave" the government, says Skadden’s Zornow. "He really is a unique talent." In addition, says Zornow, "he’s a nice guy."

Fitzgerald and Skadden declined to comment about his compensation, but two people in the Chicago legal community peg it at $3 million a year. If that’s correct, then Fitzgerald is now making in three weeks what it took him a year to earn in the U.S. attorney’s office, where he made $155,000.

Fitzgerald’s friend Leonard Gail, a commercial trial lawyer and litigator at Chicago’s Massey & Gail, says that he doesn’t think the former prosecutor struggled with the idea of going to a big law firm: "I think the question he had was whether the line he drew for his practice would be something a law firm would find acceptable." Gail is confident that Fitzgerald will excel in his new role. "Pat is a nothing-in-moderation guy. If he decided he will be a private-firm lawyer, he will be a hell of a private-firm lawyer."