After graduating in law from Sydney University in 1973 Greg was admitted as a Solicitor the same year and worked at several small firms until beginning a career in Government law. Greg mainly worked in prosecutions for the Commonwealth Crown, the Commonwealth DPP and later, after admission as a Barrister in 1987, as a NSW Crown Prosecutor and Deputy Senior Crown Prosecutor until his appointment as Deputy Director of Public Prosecutions in 2002. He was appointed to the role of Senior Counsel in 2004.
Along the way Greg worked as an instructing Solicitor to the Stewart Royal Commission into Drug trafficking, Senior Legal Adviser to the National Crime Authority and as Counsel Assisting the Independent Commission Against Corruption under Commissioner Ian Temby QC.
Greg was elected to the NSW Parliament in March 2007 as Member for Epping and shortly thereafter was appointed Shadow Attorney General, Shadow Minister for Justice, Shadow Minister for Juvenile Justice.
Greg served in the O’Farrell Government as Attorney General and Minister for Justice from April 2011 to April 2014. He retired at the 2015 elections and has returned to the Bar in order to practice in criminal law.
Greg is currently a member of the Australian Catholic Life Committee of the Australian Catholic Bishops’ Conference.
On 15 June, 2016, Archbishop Anthony Fisher OP appointed Greg a Governor of the Catholic Cemeteries Board for a period of three years. He was appointed to the position of Deputy Chair on 7 December, 2016.