John is originally from New York. He earned his bachelor's degree in liberal arts from New York University, his master's degree in government from St. John's University, and his doctorate degree in criminal justice from Rutgers University. John and his wife, Linda, have two sons and live together in Fountain Hills.

John works as a professor of criminal justice and the director of the Administration of Justice Studies and Forensic Science Program at Scottsdale Community College. He previously taught at Arizona State University and served as an officer and detective sergeant with the Port Authority of New York and the New Jersey Police Department.

John Kavanagh currently serves as the state senator for District 3. He was first elected in 2022 and is serving his first term. He is the chair of the Government Elections Committee and the vice-chair of the Appropriations Committee. Kavanagh previously served as the state representative for District 23 from 2012 to 2014 and again from 2018 to 2022. He has also previously served as a state senator, a town councilman in Fountain Hills, and a town councilman in Lafayette, New Jersey.