Peter C. Cavanagh was born in Springfield, Illinois. He received 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 practiced law from 1997 to 2008 as a general practitioner in Springfield. He served at various times 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 to the Fourth District Appellate Court in 2018. While serving as a circuit judge, Judge Cavanagh was instrumental in the creation of Sangamon County's Drug Treatment Court and presided over that Court until his assignment to the appellate court.
Justice Cavanagh is active in the Sangamon County Bar Association and served as its President in 2010. He is also an Adjunct Professor of Law and Government at MacMurray College in Jacksonville, Illinois.