Ill health affected Plunkett's schooling, he was tutored at home, and attended the Catholic University School and Belvedere and, in 1908, he went to England, and spent two years at Stonyhurst in Lancashire. He never managed to get to university although he was published from time to time in the student journals. Plunkett shared MacDonagh’s enthusiasm for literature and was an editor of the Irish Review. Along with MacDonagh and Edward Martyn, he helped to establish an Irish national theatre. He joined the Irish Volunteers in 1913 and the IRB in 1914. During the planning of the Rising, Plunkett was appointed Director of Military Operations, with overall responsibility for military strategy. Plunkett was based in the GPO during the Rising. He married Grace Gifford while in Kilmainham Gaol following the surrender.
Chuir droch-shláinte isteach ar cuid scolaíochta Phluincéid. Cuireadh oideachas air sa bhaile agus d’fhreastail sé ar an Scoil Ollscoile Chaitliceach agus ar Belvedere, agus sa bhliain 1908 chuaigh sé go Sasana, áit ar chaith sé dhá bhliain ag Stonyhurst i Lancashire. Níor éirigh leis riamh freastal ar an ollscoil cé gur foilsíodh saothair leis ó am go ham in irisí mic léinn. Bhí suim ag Pluincéad sa litríocht agus bhí sé ina eagarthóir ar an Irish Review. I gcomhar le Mac Donnchadha agus Edward Martyn, chuidigh sé le hamharclann náisiúnta na hÉireann a bhunú. Chuaigh sé isteach sna hÓglaigh in 1913 agus glacadh leis isteach san IRB sa bhliain 1914. Chuaigh sé go dtí an Ghearmáin le casadh le Ruairí Mac Easmainn in 1915. Le linn don Éirí Amach a bheith á phleanáil ceapadh Pluincéad ina Stiúrthóir ar Oibríochtaí Míleata agus freagracht fhoriomlán air as straitéis mhíleata. Bhí sé lonnaithe in Ard-Oifig an Phoist le linn an Éirí Amach. Phós sé Grace Gifford agus é i bPríosún Chill Mhaighneann i ndiaidh géilleadh lucht an Éirí Amach.