She had been held in Mountjoy since her arrest at Rathmines on 26th September. The proceedings took place at the Royal Barracks (now Collins Barracks).

Her close friends Dr. Kathleen Lynn, Maud Gonne MacBride and Hanna Sheehy-Skeffington were permitted to attend but under strict conditions.

Markievicz was charged with conspiring to ‘organise and promote’ Fianna Éireann for the purposes of ‘committing murders of military and police; the drilling of men; the carrying and using arms; and the training of recruits for the Irish Volunteers’.

When asked to plead guilty or not guilty, Markievicz replied: “I do not recognise this court. It is not constituted legally, not being based on the authority and will of the people of Ireland but on the armed force of the enemies of the Irish Republic”.

A plea of not guilty was then formally entered.

The prosecution outlined the reasons why Fianna Éireann was such an unlawful organisation:
“It advocated the unlawful carrying of firearms and the inciting of His Majesty’s subjects to become disaffected, and the preventing of the law of force by arms. Its objective was the murder of His Majesty’s officers, and the furnishing of recruits for the Irish Volunteers, which was unquestionably in itself an unlawful organisation.”

The trial lasted two days and she was found guilty of all charges. She was sent back to Mountjoy to await sentencing.