John Hayes was born in Clegg, Glandore, County Cork in 1888, the son of Denis Hayes, a farmer. He joined the civil service working as a sorter in the GPO, London from 1904 to 1912, returning to work in Dublin following that time. Subsequently, working in Skibbereen for the weekly Southern Star as an editor and a manager. He was a participant in the 1916 Easter Rising at the GPO, Dublin, for which he was arrested and spent time interned in Wormwood Scrubs.[3]
Hayes was arrested by the British forces during a raid on party offices in Dublin in November 1919. As a result, he was sentenced to three months imprisonment. He was re-arrested in 1920 during the War of Independence. He was a member of the Irish Republican Army. He was also reputedly a member of Tom Barry's Flying Column in West Cork.