Peter C. Cavanagh was born in Springfield, Illinois. He earned a B.S. degree in history from Illinois State University and a J.D. degree from the John Marshall Law School. Prior to taking the bench, Justice Cavanagh primarily practiced law from 1997 to 2008 as a general practitioner in Springfield. He served as an Assistant State's Attorney in Cook and Sangamon Counties and an Assistant Public Defender in Sangamon and Logan Counties.
Justice Cavanagh was appointed resident Circuit Judge of the Seventh Judicial District by the Illinois Supreme Court in 2008. He was elected, and later retained, to that position prior to being assigned and then elected to the Fourth District Appellate Court in 2018. While serving as a circuit judge, Judge Cavanagh was instrumental in the creation of the Sangamon County's Drug Treatment Court and presided over that Court until his assignment to join the appellate court. Justice Cavanagh represents the Fourth District on the Illinois Appellate Court Workers' Compensation Commission Division.
Justice Cavanagh is active in the Sangamon County Bar Association and served as its President in 2010. He has also served as an Adjunct Professor of Law, Policy, and Government at area colleges. Justice Cavanagh is the son of former Sangamon County State's Attorney and Chief Circuit Judge C. Joseph Cavanagh.