He emigrated to Queensland, and went to Cooktown in 1876, where he was appointed government medical officer; in 1877, he was in Thornborough.
He joined the Volunteer Defence Force in 1881, as surgeon to the Artillery.
In that year he visited England as the representative of the North Queensland Separation League; and much of the progress which has since attended the operations of the League is to be ascribed to the impetus given to it by Dr. Ahearne's exertions.
[1] Ahearne served as a colonel of the medical in a contingent of the Queensland Land Force in the Boer War [clarification needed – There were two.
[2] As a lieutenant colonel in April 1907, he became the medical officer for the No.5 Queensland Battalion of the Commonwealth Cadet Corps.