Born in Louisville, KY, Gaghan was raised by his mother, Elizabeth, and his father, Stephen, whom she divorced in 1980. He attended the Kentucky Country Day School, a Louisville-based college preparatory school where he was a member of the state's all-star soccer team before beginning his descent into alcohol and drug addiction. On his last day of his senior year, Gaghan was expelled from Kentucky Country Day for allegedly driving a go-cart through the hallways. After later receiving his GED, he went to the University of Kentucky before attending Babson College, a private business school in Massachusetts. Because he was the grandson of Jerry Gaghan, a newspaper columnist and critic for both Variety and the Philadelphia Daily News, Gaghan harbored ambitions to become a writer. Eventually, he connected with writing partner Michael R. Perry, and made his debut on the small screen with a script for an episode of "New York Undercover" (Fox, 1994-98). The pair quickly segued to the positions of story editor and writers for the short-lived cult drama "American Gothic" (CBS, 1995-96) and the acclaimed procedural "NYPD Blue" (ABC, 1993-2005). During their one-season stint on "NYPD Blue," Gaghan and Perry shared an Emmy Award with executive producer David Milch for the "Where's Swaldo?" episode. Meanwhile, the writing team moved over to David E. Kelley's successful legal drama, "The Practice" (ABC, 1997-2004), where they collaborated as story editors and occasional script writers, only to move on again and find their momentum tempered by the quickly cancelled "Sleepwalkers" (NBC, 1997). But by this time in his life, Gaghan's drug addiction began taking its toll. Having been arrested some 20-30 times over the years on various misdemeanor charges, Gaghan found himself staring death in the face on several occasions. He once tried to rob a crack dealer, only to have the tables turned when the dealer pulled a gun. Another dealer went so far as to put a knife to his throat. While those experiences were not enough to convince him to change course, Gaghan hit rock bottom when he discovered over the course of five days that all three of his heroin dealers had been arrested, leaving him high and dry. While locked in the bathroom contemplating suicide, Gaghan found the strength to call a friend who happened to be the only person he knew that had quit drugs. His reaching out marked Gaghan's start upon the long road to recovery.Gaghan segued to the big screen with his first writing credit on the horror sequel "I Still Know What You Did Last Summer" (1998). He moved on to write "Rules of Engagement" (2000), an old-fashioned military courtroom drama directed by William Friedkin and based on an idea from former U.S. Navy Secretary James Webb. Though the film enjoyed some success, it was nothing compared to his second screenplay of that year. For "Traffic" (2000), helmed by Steven Soderbergh, Gaghan turned a six-hour British television miniseries from 1989 into an engrossing, multilayered, critically acclaimed examination of the seeming futility of the War on Drugs. Drawing from his own experiences as an addict, Gaghan wove together the strands of three separate stories on both sides of the Mexican-U.S. border: a relatively honest Tijuana cop (Benecio Del Toro) struggling to balance his professional loyalties with his personal ethics; a San Diego socialite (Catherine Zeta-Jones) who takes over her husband's drug smuggling business after facing the threat of losing everything; and an Ohio jurist (Michael Douglas) newly appointed as the nation's new drug czar, who finds himself fighting a war on drugs much closer to home when his teenage daughter (Erika Christensen) succumbs to addiction. Both richly complex and deeply intimate, "Traffic" struck a chord with both audiences and critics, becoming not only a box office hit, but also an Oscar winner, with Gaghan being rewarded with the Academy Award for Best Adapted Screenplay.Gaghan was in demand following his triumph with "Traffic," particularly as a script doctor, which led to writing uncredited drafts for movies like "Black Hawk Down" (2001) and "Phone Booth" (2003). He made his directing debut with the thriller "Abandon" (2002), crafted from his script about a reckless college student (Charlie Hunnam) whose disappearance leads a detective (Benjamin Bratt) to conclude something more sinister has happened. He moved on to write "The Alamo" (2004), an overinflated endeavor about the famed battle during the Texas Revolution that earned considerable critical scorn en route to becoming one of the biggest box office flops in cinema history. After receiving story credit on the teen-themed melodrama "Havoc" (2005), Gaghan assumed the director's chair for the second time for "Syriana" (2005), another complicated, multi-character exploration of a politically charged subject: this time the behind-the-scenes machinations over Middle Eastern oil. The result was an intriguing exploration of the issue through various points of view, including a burnt-out CIA agent (George Clooney) abandoned by the government he served; an idealistic analyst (Matt Damon) who becomes obsessed with helping an oil-rich nation develop after the death of his son; and a canny attorney (Jeffrey Wright) investigating the propriety of an oil deal. The result was another critically acclaimed hit that earned Gaghan a nomination for Best Original Screenplay at the Academy Awards. After several years removed from feature filmmaking, Gaghan returned to television as the creator of "S.I.LA." (NBC, 2011-), a procedural that followed the intertwined worlds of politics, law enforcement and crime in contemporary Los Angeles.