He was educated at private schools, and entered the South Australian Civil Service, receiving his first appointment from Sir Richard Graves MacDonnell, the then Governor.
After passing ten years in the Audit Office, and rising to the third position in that department, he was promoted to the clerkship of the Executive Council, being at the same time gazetted Clerk to the Court of Appeals.
In consequence of certain reductions in the estimates, which involved several departmental changes, O'Halloran retired from the Government service in 1871, with compensation for loss of office, the Governor in Council recording his testimony to the honourable manner in which he had discharged his duties.
[1] In 1873 he proceeded to New Zealand, and travelled through both islands, collecting information in connection with some elaborate investigations which had been conducted in London with a view to the application of an improved process for the extraction of the fibre of the Phormium tenax.
He was married, at the parish church, Cheltenham, Gloucestershire, England, on 17 August 1886, to Alice Mary, daughter of the Henry Simpson, of "Ridge Park", Glen Osmond, South Australia.