Stephen grew up in the Illawarra and is one of five kids from a working-class family.

Stephen's father taught at the local TAFE and his mother worked as a school assistant.

"I grew up in Wollongong, in a big Catholic family. There was always lots of kids, lots of noise, lots of sport, not so much money, but a strong commitment to working hard, getting a good education, and making a contribution to the community that you live in."

Stephen attended St Brigid's Primary School, Gwynneville, before attending Edmund Rice College in Wollongong, where he graduated as Dux and School Captain.

He completed a BA (History and Politics) at the University of Wollongong, while working on various local health services and youth projects, before moving on to a law degree.

Stephen stepped down as the National Secretary of the Community and Public Sector Union CPSU, one of Australia's largest and most progressive unions in 2010 to focus on his election campaign. He was the National Secretary for over five years and a union representative for over 15 years.

Stephen was the member for Throsby until the 2016 redistribution, where Throsby became the electorate of Whitlam.