Career
He was elected as a Sinn Féin Member of Parliament for the Cork City constituency at the 1918 general election. In January 1919, Sinn Féin MPs refused to recognise the Parliament of the United Kingdom and instead assembled at the Mansion House in Dublin as a revolutionary parliament called Dáil Éireann, though de Róiste was unable to attend. De Róiste opposed the Belfast Boycott stating in a 1920 Dáil debate.
"it would mean having to purchase English-made goods instead of Belfast-made articles
Economic penetration was the solution of the Ulster question. In April, 1921 while staying at a neighbours for fear of assassination, the family home was stormed by a party of Black and Tans.
The intruders left unopposed. De Róiste was re-elected without contest at the 1921 elections for the Cork Borough constituency.
He supported the Anglo-Irish Treaty and voted in favour of lieutenant
He did not stand at the 1923 general election but stood unsuccessfully as a Cumann na nGaedheal candidate at the June 1927 general election. In his private life he was Secretary and Director of the Irish International Trading Corporation, Cork, and an author