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

This man signed the Declaration of Irish Independence. He was one of the most prominent of the leaders of the Irish Volunteers and attended at the meetings of the Executive and Control Councils. He wrote and sent despatches and mobilisation orders for and to the rebels during the rebellion and he surrendered with a body of rebels in Sackville Street with whom he had been operating for the previous week.

Sean MacDermott was tried by Field General Courts Martial on 3 May 1916. The proceedings are contained in the PRO document WO 71/344.

Court Martial Proceedings

The members of the courts martial were Colonel D. Sapte (President), Lieutenant-Colonel Bent and Major F.W. Woodward.

At his trial, Sean MacDermott faced two charges to which he pleaded not guilty:

1. " ... 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."
2. "Did attempt to cause disaffection among the civilian population of His Majesty."

The 1st Witness was Constable Daniel Hoey (Dublin Metropolitan Police) who stated

I have known the accused by the name of John McDermott, or in the Irish form Sean MacDiarmada, for 3.5 years. The accused associated with leaders of the Irish Volunteers, Thomas Clarke, P.H. Pearse, Joseph Plunkett, Frank Fahy, Joe McGuinness, E.J. Duggan and others. They held executive meetings once a week and General Council meetings once a month at HQ Irish Volunteers, 2 Dawson Street. The accused and those mentioned attended these meetings. The accused visits an office in 12 D'Olier Street Dublin frequently. It has the name Sean MacDiarmada on a plate. I have seen some of the others mentioned visiting there; Thomas J. Clarke had a tobacconist's shop at 75a Parnell Street. This shop was frequented by leading members. I have seen the accused there frequently. I did not see the accused at Liberty Hall, the headquarters of the General Transport and Workers Union.

After being questioned by the accused the witness made the following statement:

I have only known the accused to associate with Irish Volunteer leaders during the last 12 months. I have known him for 3.5 years but at first he did not so associate as far as I know. I do not know all the objects of the Gaelic league but I understand the Irish Language is one of them. I do not know his connection with the Gaelic League, I have not enquired into it. I have not seen the accused at the Hd. Qrs. Gaelic league.

The report of the Central Executive meeting of the Irish Volunteers is published in the "Irish Volunteer". A paper known as Nationality is published at 12 D'Olier Street. This is the accused's principal means of livelihood. There are several offices in 12 D'Olier Street. Clarke's shop sells papers etc as well as tobacco. He did a good business there. I have seen the accused visit many public houses and remain a considerable time.

The 2nd witness was Lieutenant W.H. Ruxton (3rd Royal Irish Regiment) who stated

I was on duty in Parnell Street on the 29th April 1916 when 3 parties of rebels: two armed and one partially armed with knives and some ammunition, surrendered. The accused was one of the two armed parties who surrendered between 6 and 7 pm. The accused spoke to me and said he would not be able to march far on account of his leg. I asked him why he could not march. One of the others told me his leg was paralysed. I asked the accused "How did you get into this affair". The accused replied to the effect that he had his place in the organisation. The parties came from the direction of the General Post Office. They were sent on to the Rotunda. I am positive the accused is the man I spoke to.

When Lieutenant Ruxton was cross-examined by the accused he stated that there were about 200 men in the accused's party. They were not all armed. I did not see any arms in the accused's possession.

The 3rd witness 2nd Lieutenant S.A.L. Downing (3rd Royal Irish Regiment) who stated

I was on duty on 29th April 1916 in Sackville Street. I took the names of about 23 of the rebels after they had laid down their arms. The accused was in that party and is shown on the list, but I do not know if he actually gave the name.

When cross-examined by the accused, 2nd Lieutenant Downing admitted that he did not pay particular attention to the surrender of arms and did not see the accused with any arms.

The 4th witness was Lieutenant-Colonel H.F. Eraser (21st Lancers) who stated

I was present in the Richmond Barracks Dublin on the 30th April 1916, and identify the accused as one of those confined there, but not necessarily on that date. All papers taken from the prisoners on this occasion were handed to me. I identify the paper produced as one of those handed in to me in the gymnasium on that day.

The 5th witness was Edward Gaunon (Warden Mountjoy Prison Dublin) who stated

I identify the accused as John McDermott who was confined in Mountjoy Prison Dublin in May/June 1915. I produce the cash and property book, in which the accused signed his name Sean McDiarmada on the 26th May 1915. The spelling is the same as on the document now shown to me. Except for the S, there is a strong resemblance between the signatures.

When cross-examined by the accused Gaunon admitted that he was not a fluent Irish scholar.

The 6th witness was Captain Henry de Courcey Wheeler who stated

On 7 May 1916 at about 6.30pm I searched ...

[part of record is missing]

... the voice of a man named McDermott, not the accused, but a man I had not known before, I did not attend the weekly meetings of the Irish Volunteers, nor any of their meetings. I sent them their accounts by post.

Court Martial Verdict

Sean MacDermott was found guilty of the 1st charge and not guilty of the 2nd. He was sentenced to death by shooting. The sentence was confirmed by General Maxwell.

At 3.45am on 12 May 1916, Sean MacDermott was shot in the former stonebreakers yard at Kilmainham Prison. His remains were later buried in Arbour Lane Cemetery.