Born in Brooklyn in 1935 as the first of seven children to immigrants from Belfast, Northern Ireland, Hamill attended Catholic schools throughout his childhood. More in tune with the city streets than the schoolroom, he dropped out at age 16 to labor in the Brooklyn Navy Yard as a sheet metal worker, and from there signed up with the United States Navy, where he was able to complete his high school education. Using the educational benefits of the G.I. Bill of Rights, he attended Mexico City College in 1956-1957, studying painting and writing.

While Hamill fell in love with Mexico (and would eventually come to consider it his second home), his interest in design brought him back to New York to study at Pratt Institute, and work as a graphic designer. However, in 1960, he made the fateful career move that would change his life: taking a job as a reporter for the New York Post. Hamill's pavement-pounding work made him a crafty chronicler of city life -- from the grimy streets of the crime beat to the great domestic disturbances of the 1960s -- and he graduated to columnist, writing extensively on art, jazz, immigration, sports, city life and politics. Hamill has been a columnist for the New York Post, the New York Daily News, New York Newsday, the Village Voice, New York Magazine, The New Yorker and Esquire. Perhaps one of Hamill's most intriguing achievements in New York journalism is the fact that he served as editor-in-chief of both the New York Post and the New York Daily News -- the city's two most notoriously competitive dailies.

Hamill's nonfiction books have resonated with readers craving more than a few column inches. His 1994 bestselling memoir, A Drinking Life, was, as Publishers Weekly noted, "not a jeremiad condemning drink... but a thoughtful, funny, street-smart reflection on its consequences." Turning his attention to other lives, Hamill has also written tributes to idols Frank Sinatra (1998's Why Sinatra Matters) and Mexican painter Diego Rivera (1999's Diego Rivera). Among his other nonfiction, Hamill has published two collections of his journalism (Irrational Ravings and Piecework) and an extended essay on journalism called News Is A Verb. In 2004, he published to much critical acclaim, Downtown: My Manhattan, a non-fiction account of his love affair with New York.

Hamill has also enjoyed critical and commercial success as a fiction writer, with ten novels and two collections of short stories. His 1997 novel, Snow in August, was an instant New York Times bestseller, remaining on that list for four months. On the gritty coming-of-age story, the Times observed, "Mr. Hamill has told versions of this story many times, in fiction and journalism. His widely praised bestseller, Forever (2003), is the magical, epic tale of an extraordinary man who arrives in New York in 1740 and remains…forever. His latest 2007 novel, North River, tells the story of a doctor's professional and personal struggles in the icy grip of the Depression.

Hamill is the father of two daughters, and has a seven-year-old grandson. He is married to Japanese journalist Fukiko Aoki, and they divide their time between New York City and Cuernavaca, Mexico. Hamill is a Distinguished Writer in Residence at New York University and is writing a new novel.