Following the
Easter Rising of 1916, he joined the
IRA, becoming an Officer in the 3rd battalion of the Dublin Brigade. Gallagher collaborated with
Erskine Childers to publish the
Irish Bulletin alongside the Republican publicity staff and fought alongside
Éamon de Valera during the
Irish War of Independence. Gallagher served as director of publicity for
Sinn Féin in the days leading up to their landslide victory in the
1918 United Kingdom general election in Ireland Gallagher and
Robert Brennan were the significant contributors to the Irish Bulletin which was produced at this time. He wrote several short stories for de Valera under various pseudonyms. Gallagher served long stints in prison due to his
IRA involvement and went on many hunger strikes (the shortest lasting three days, the longest 41). In the 1920s Gallagher and thousands of other Irish Republican prisoners went on hunger strike to protest their
internment without charges/trials and prison conditions. (See:
1923 Irish hunger strikes). Gallagher led approximately 100 interned men on a successful 14 day hunger strike demanding
Prisoner of War status or release (they were released). In his day to day journal while on
hunger strike, Gallagher writes about his motivations on the first day of the strike (April 5, 1920) in
Mountjoy Prison on (
Easter Monday): "There is a queer happiness in me. If it were not so quiet in this cell and in the whole jail, I would sing and call out in sheer gaiety of spirit...The fight is on, the fight that now can have but one ending...triumph and freedom, something done for liberty and the rights of all men." ==Later life==