After experiencing the political and social turmoil in Ireland after the 1913 Dublin Lockout and the 1916 Easter Rising, Byrne became an active member of the Postal Trade Union.
Because he didn't recognize the legitimacy of British Officers holding court over an Irish citizen, he denied entering a plea or even participating in the trial itself.
The volunteers left the hospital with the gravely injured Byrne, but the escape car and driver had in the meantime been ordered to another IRA operation and so they stopped a horse carriage at Hasset's Cross.
The occupants of the carriage, John Ryan of Knockalisheen and his wife, brought the bleeding and injured Byrne to their house, put him to bed and called for medical and clerical assistance.
After a doctor, John Holmes, had arrived and examined Byrne, a large bullet wound on the left side of his body was found, which had perforated his lung and his abdomen.
Nevertheless, the funeral procession was accompanied by huge crowds and his remains, which lay in state in front of the high altar in St John's Cathedral, were visited by thousands from Limerick and surrounding areas.