O'Loughlin was born in Canberra. His year of birth has been given, variously, as 1975, 1976, 1977, and 1978. His father is a physics teacher in Sydney and his mother is a nurse.
O'Loughlin suffered from asthma, attention deficit hyperactivity disorder and obsessive compulsive disorder.
He was educated at Macquarie Primary School with his sister Jennifer who is a year or two younger than him.
As a boy he wanted to become a jet fighter pilot when he grew up, but was told by his teacher that it was an unlikely dream as he suffers from asthma; this was a painful memory for him that recently evoked the response, "Always teach children to reach for the stars."
Playing dress up with items out of an old trunk was one of his favorite pastimes . He has fond memories of often donning a white clown suit with big red polka dots.
School was a continuous struggle, caused by learning difficulties that were compounded by ADHD and OCD, and he left when he was 14, after which he held all manner of jobs in a wide range of fields.
He enrolled at the National Institute of Dramatic Art. Despite a challenging first year, he went on to graduate from NIDA in
June 2002, after completing their highly competitive three-year, full-time Bachelor of Dramatic Art program, to which only a limited number of students are accepted annually.
