Keane was born on 14 February 1881 in Beechworth, Victoria, the fourth child of Hanorah (née O'Sullivan) and Timothy Keane. His parents were Irish Catholic immigrants – his mother was born in County Tipperary and his father, a police constable, in County Kerry. He possessed papers showing that his father had served with the Union in the American Civil War under the name "Timothy Kane", and had received a commendation for his role in the Battle of Sailor's Creek.