He was the oldest of five children born to Sarah (née Goodman) and Joseph Henry Opas; his father was an accountant.

[1][2] Opas grew up in the suburb of St Kilda,[3] attending Melbourne Church of England Grammar School until the age of 15.

[4] Following Ryan's execution, Opas was charged with unprofessional conduct by the Ethics Committee of the Victorian Bar Council in connection with his public appeals for assistance with the case.

He was prosecuted by Ninian Stephen but retained Richard McGarvie and Ivor Greenwood in his defence and had the charges dismissed.

[4] He was disillusioned by the experience and left the bar for four years to work as group legal officer for Conzinc Rio Tinto of Australia.