Mastro was raised in New Jersey and clerked for Justice Alan Handler of the New Jersey Supreme Court after graduating from U. Penn's law school. He went on to spend three years as an associate at Cravath (working with David Boies on the seminal case Westmoreland v. CBS) before leaving to become an Assistant U.S. Attorney for the Southern District, where he met Rudy Giuliani. The two worked together for several years prosecuting organized crime figures and drug traffickers, and when Rudy was elected mayor in 1994, he hired Mastro as his chief of staff. In 1996, Giuliani named him the city's Deputy Mayor of Operations. Mastro left the administration two years later, moving into private practice as a partner at Gibson, Dunn & Crutcher in 1998.
As deputy mayor, Mastro spearheaded Giuliani's efforts to clean up Times Square and loosen the mob's stranglehold on the San Gennaro Festival and the Fulton Fish Market. (Mastro says he got death threats for the latter, and had to hire bodyguards to protect himself and his family.) Since returning to private practice at Gibson, Mastro has litigated dozens of civil and criminal cases, butting heads with his former employer—the City of New York—on more than one occasion. He battled against Mayor Bloomberg's efforts to move the Fulton Fish Market to the Bronx as well as his proposal to build a West Side stadium. (He was retained by Cablevision's chief, Jim Dolan.) Following Sept. 11th, he represented several dozen families of firefighters who perished in the tragedy in their suits against the city.
Mastro has taken on a handful of bizarro cases as well. When former Supreme Court nominee Robert Bork sued the Yale Club for more than a $1 million after a trip and fall accident in June 2006, it was Mastro who led the charge. (The blog Overlawyered described the case as "embarrassingly silly.") He also represented Martina Hingis in her suit against a sneaker company (she claimed the shoes had "injured" her feet) as well as Anna Kournikova, who sued Penthouse over nude photos published in the magazine. Other—more serious—Mastro clients over the past few years have included Bear Stearns, Dow Jones, UBS, Lehman Brothers, and Bruce Ratner's development firm, Forest City Ratner.
Not surprisingly, Mastro played an active role in his former boss's sorry campaign for president. Four partners at Gibson Dunn were on Giuliani's "Justice Advisory Committee," including Mastro and Gibson partner Theodore Olson, a former solicitor general in the George W. Bush administration (and the lawyer who went head-to-head with David Boies in Bush v. Gore). Mastro helped Giuliani both by raising money and speaking out on his behalf to the press.
Mastro is married to Jonine Bernstein, an epidemiologist at Memorial Sloan-Kettering. The couple has a daughter, Arianna, and lives on West 9th Street.