Margolin, who grew up in New York City and Levittown, New York graduated from The American University in Washington, D.C. with a Bachelor's Degree in Government. From 1965 to 1967, he volunteered with the Peace Corps in Liberia, West Africa. In 1970, he graduated from New York University School of Law, the last two years which he financed by teaching junior high school in the South Bronx during the day. His first job after law school was a clerkship with Herbert M. Schwab, the Chief Judge of the Oregon Court of Appeals. From 1972 until 1996, he was in private practice specializing in criminal defense at the trial and appellate levels. As an appellate attorney he appeared before the United States Supreme Court, the United States Court of Appeals for the Ninth Circuit, the Oregon Supreme Court and the Oregon Court of Appeals. As a trial attorney, he handled all sorts of criminal cases in state and federal court and has represented approximately 30 people charged with homicide, including several who have faced the death penalty. Margolin was the first Oregon attorney to use the Battered Women's Syndrome to defend a woman accused of murdering her spouse. 

Since 1996, Margolin has been writing full-time. All of his novels have been best sellers. His novels have been made into an HBO movie (The Last Innocent Man) as well as a mini-series (Gone But Not Forgotten). He has been recognized by the Mystery Writers of America, been nominated twice for the Oregon Book Award and published by more than 25 foreign publishers. His short stories and non-fiction articles have been included in magazines and law journals and his short story, The Jailhouse Lawyer, was selected for the anthology 1999, The Best American Mystery Stories. 

From 1996 to 2009 Margolin was the President and Chairman of the Board of Chess for Success. He is still heavily involved in the program. Chess for Success is a non-profit charity that uses chess to teach elementary and middle school children in Title I schools study skills.