In his law practice, he is best known for bringing the case of Victims of Sabra and Shatila v. Ariel Sharon et al., under the law of universal jurisdiction in Belgium, where he won a judgment against the accused before a change in Belgian law removed the jurisdiction of the court. As a democratic activist, he was involved with the Iraqi opposition to Saddam Hussein, even spending time in an Iranian jail after organizing international monitoring of the first free elections ever in Iraq, in May 1992. Mallat helped establish the Middle East regional office of Amnesty International in Beirut in 1999 for which his office has acted since as its legal counsel. He is a frequent op-ed contributor in newspapers ranging from the Nahar (Lebanon) to the New York Times, and has held research and teaching positions at Yale Law School, London University, Virginia Law School, the University of Lyon, the Library of Congress, the Saint Joseph University and the University of California Boalt School of Law. He spent one year at Princeton University where he was a Visiting Professor in the Woodrow Wilson School, Fellow in the Program in Law and Public Affairs, Fellow in the University Center for Human Values, Fellow in the Program in International and Regional Studies and a Distinguished Visitor in the Bobst Center for Peace and Justice.

In 2007, he moved to Utah and became a professor at the law school at the University of Utah.

He is the editor of over twenty books and his articles in English, French and Arabic have been published in academic journals around the world and he served as a joint general editor for five volumes of the Yearbook on Islamic and Middle Eastern Law.

He currently resides in Salt Lake City, Utah with his wife and his younger son. His father is Wajdi Mallat, the first president of the Constitutional Council (Arabic ?????? ????????) of Lebanon, from 1994 to 1997.