A biographical note from 2007 stated that Costello "laid the ground-work for Australia's prosperity since 1996... Peter was educated at Monash University and, for a time, was a part-time teacher in law and economics/politics as well as a member of the University Council. Prior to entering Parliament, he was a barrister. He was counsel in some of Australia's best-known industrial disputes and was a regular advocate in National Wage cases. Peter is the Member for Higgins. He is married to Tanya and they have three children. He describes his favourite activity as cooking on the barbeque at home (badly) and following his beloved football team (passionately)."  (Costello has since resigned from Parliament).
His brother is Tim Costello.
- Helped found the HR Nicholls Society