Greg was born and raised in Dubbo, NSW along with his two brothers Brett and Joseph. He remained in Dubbo until his enlistment into the Australian Regular Army in 1990 and was schooled at St John's College. Greg's father was a hospital maintenance worker and his mother Mary is retired from her role as a special needs worker for people with intellectual and physical disabilities. Greg and his wife Simone are raising their two boys in Mt Annan where they moved upon Greg's military discharge in 1998. He is currently employed as a NSW/ACT Operations Manager in the business logistics field.
Greg was preselected as Labor's candidate for Campbelltown in the first ever community preselection held in the seat of Campbelltown in March 2014.