In a memorandum sent by General Sir John Maxwell to the then British Prime Minister, Herbet Asquith, the following description was provided for William Pearse:

This man was a brother of P.H. Pearse, the President of the Irish Republic. He was associated with the Sinn Fein movement from its inception. He held the rank of Commandant in the rebel army. He was present in the GPO during the fighting and was acting as an officer and surrendered with the rebels in Sackville Street.

William Pearse was tried by Field General Courts Martial on 3 May 1916. The proceedings are contained in the PRO document WO 71/358.

Court Martial Proceedings

The members of the courts martial were Colonel E.W.S.K. Maconchy (President), Lieutenant-Colonel A.M. Bent and Major F.W. Woodward.

To the charge of " ... did take part in an armed rebellion and in the waging of war against His Majesty the King, such act being of such a nature as to be calculated to be prejudicial to the Defence of the Realm and being done with the intension and for the purpose of assisting the enemy."

William Pearse was the only person tried for his part in the Easter Uprising who pleaded guilty. He also tried with three other men: John Dougherty, John McGarry and J.J. Walsh who all pleaded not guilty.

The 1st witness was 2nd Lieutenant S.L. King (12th Royal Inniskillen Fusiliers) who stated

On Tuesday 25 April at 11am I was seized by two armed men outside Clery's shop opposite the General Post Office. John Dougherty was one of the two. He held a revolver at me and told me if I did not put my hands up h would blow my brains out. He took me to the General Post Office where I was held as a prisoner till Friday night. I was in uniform. I saw each of the other prisoners in the GPO while I was there and during that time the Post Office was held against His Majesty's troops by men firing against the troops. There was another officer there Lieutenant Chalmers who was wounded, also in uniform. I know that William Pearse was an officer but do not know his rank. I do not know what McGarry's position was. He was not in uniform. J. Walsh did not appear to be in any authoritive position but was dressed in uniform. I saw Pearse, McGarry and Walsh wearing equipment, belts and pouches. Dougherty had a revolver but no equipment. It was Dougherty who threatened to blow my brains out, not the man with him. I am quite certain that I saw McGarry with equipment on.

John Dougherty did not call any witnesses in his defence but made the following statement:

I did not say that I would blow Lieutenant King's brains out.

William Pearse did not call any witnesses in his defence but made the following statement:

I had no authority or say in the arrangements for the starting of the rebellion. I was throughout - only a personal attache to my brother P.H. Pearse. I had no direct command.

John McGarry did not call any witnesses in his defence but made the following statement:

I had no intension of assisting the enemy. I had no position or rank of any sort. I was employed as a messenger I did not know of the rebellion until the Post Office was taken. I had no rifle.

J.J Walsh did not call any witnesses in his defence but made the following statement:

During the past eighteen months I have held no official position either big or little in the Irish Volunteers or any other national movement and my whole attension was confined to business. I gave it up at the time of the split between the Redmondites and the Irish Volunteers. I mean my official position. I remained in the Volunteers as a private and on being mobilised on Monday I knew nothing whatever of the intension of the mobilisation. I fired on nobody during the time in the Post Office. I had no arms whatever. I was told off to attend to the water and sand arrangements in case of fire.

Court Martial Verdict

All four men were sentenced to death by shooting. The sentences on Dougherty and Walsh were commuted to terms of ten years penal servitude and the sentence on McGarry was commuted to eight years penal servitude. However the sentence on William Pearse was confirmed by General Maxwell.

Between 4 and 4.30am on 4 May 1916, William Pearse was shot in the former stonebreakers yard at Kilmainham Prison. His remains were later buried in Arbour Lane Cemetery.