Hayes is born in Enniscorthy on December 26, 1902. During the Irish War of Independence (1919-21), he is commandant of the Wexford Brigade of Fianna Éireann. He takes the Anti-Treaty side during the Irish Civil War (1922-23), during which he is interned.
Hayes is active in Gaelic Athletic Association circles in Wexford. In 1925, he helps Wexford win the Leinster Senior Football Championship. He also serves as secretary to the county board for ten years, from the 1920s to 1930s.
Hayes joins the IRA and is on the IRA Army Council in January 1939 when it declares war on the British government. When IRA Chief of Staff Seán Russell departs on IRA business to the United States, and subsequently to Nazi Germany, Hayes becomes IRA Chief of Staff. His time in office is marred by controversy and it is widely believed that he serves as an informer to the Garda Síochána.
Hayes sends a plan for the invasion of Northern Ireland by German troops to Germany in April 1940. This plan later becomes known as Plan Kathleen. He is also known to have met with German agent Hermann Görtz on May 21, 1940 in Dublin shortly after the latter’s parachuting into Ireland on May 5, 1940 as part of Operation Mainau. He is known to have asked Görtz for money and arms to wage a campaign in Northern Ireland, although shortly after this meeting the original Plan Kathleen is discovered. The discovery of the plan leads to the acceleration of joint British and Irish military planning for a German invasion known as Plan W.
Another meeting on August 15, 1940 on Rathgar Road, Dublin organised by Hayes and attended by senior IRA men Paddy McGrath, Tom Harte and Tom Hunt, is also raided by the Garda Síochána.
McGrath and Harte are both arrested and tried by Military Tribunal, established under the Emergency Powers Act 1939. They challenge the legislation in the High Court, seeking a writ of habeas corpus, and ultimately appeal to the Supreme Court of Ireland. They are represented in the courts by Seán MacBride. The appeal is unsuccessful and they are executed by firing squad at Dublin’s Mountjoy Prison on September 6, 1940.
On June 30, 1941, Northern-based IRA men kidnap Hayes, accusing him of being a spy. By his own account, he is tortured and “court-martialed” for “treason” by his comrades, and would have been executed, but he buys himself time composing an enormously long confession. He manages to escape on September 8, 1941, and hands himself in to the Garda for protection.
The Officer Commanding (O/C) of the IRA Northern Command, Seán McCaughey, is convicted on September 18, 1941 of the kidnapping. After a long hunger and thirst strike in Portlaoise Prison, he dies on May 11, 1946.
Hayes is later sentenced to five years’ imprisonment by the Special Criminal Court on account of his IRA activities.
Within IRA circles, Hayes is still considered a traitor and an informer. One of the main allegations against him is that he informed the Garda Síochána about IRA arms dumps in Wexford. However, this is later blamed on a Wexford man named Michael Deveraux, an officer of the Wexford Battalion of the IRA who is subsequently abducted and executed by an IRA squad in County Tipperary on Hayes’ orders. George Plant, a Protestant IRA veteran, is later executed in Portlaoise Prison for Devereux’s murder.
After his release, Hayes resumes his clerical position at Wexford County Council. He dies in Enniscorthy on December 28, 1974.