Born in Quin, Ireland, Hannan was the son of John Hannan and Bridget Lynch. He emigrated to Australia in 1863.
Hannan, Tom Flanagan and Daniel Shea discovered gold near Mount Charlotte less than 40km from the Coolgardie Goldfields. After registering his claim an estimated 700 men were prospecting in the area with three days.
In 1904, at the age of sixty-one, having prospected for all his adult life, Hannan was granted an annual pension of £100 by the Western Australian Government. He ceased his propecting activities in 1910, and moved to live with two nieces in Brunswick, Melbourne. He died there in 1925.
The main street and a suburb in Kalgoorlie both bear his name and a well known statue of him is erected there also.