Before becoming a professor at the University of Mississippi, Rychlak was an attorney with Jenner & Block in Chicago. He clerked for Judge Harry W. Wellford of the United States Sixth Circuit Court of Appeals.

In 2003 Rychlak served as an academic fellow at the Foundation for the Defense of Democracies, and he studied counter-terrorism in a program in Israel. In 2004, the State Department sent him to Paris in order to address a meeting of the Organization for Security and Cooperation in Europe on the issue of free speech on the Internet. He is a signatory to the Nashville Declaration on the Church and the Holocaust and as such was honored by the U.S. Holocaust Museum in 2007. In 2008, the Roman Catholic Archdiocese of Zagreb presented him with a Blessed Cardinal Stepinac medal for his historical work.

Rychlak's memberships include the Phi Kappa Phi Honor Society, the National Association of Scholars, the editorial board of The Gaming Law Review, the Society of Catholic Social Scientists, the Fellowship of Catholic Scholars, the International Masters of Gaming Law, and the International Brotherhood of Magicians. He was appointed by the Mississippi Supreme Court to be a member of the committee working on a revision of Mississippi's criminal code, and he is a member of the Mississippi Advisory Committee to the U.S. Civil Rights Commission.

Rychlak advises the Permanent Observer Mission of the Holy See to the United Nations on various issues of international law. He also serves as a delegate at the meetings of the Assembly of States Parties to the International Criminal Court. He is the author or co-author of seven books and numerous articles. He is also a panelist for The Washington Post’s “On Faith” blog and a columnist for Crisis magazine online (hosted on InsideCatholic.com).

His most recent book, co-authored with his colleague David Case, is Environmental Law, part of the Oceana Law for the Layperson series put out by Oxford University Press. His books Righteous Gentiles: How Pius XII and the Catholic Church Saved Half a Million Jews from the Nazis (Spence Publishing, 2005) and Hitler, the War, and the Pope (Genesis Press, 2000), address the claim that Pope Pius XII failed to stand up for the victims of Nazi aggression in World War II. He often speaks and writes on that topic.