During his early years as Archbishop, at the time of the Irish Civil War, he tried to bring about peace by calling a conference of the leaders, but no basis for agreement could be found.

Arguing that the majority of the Irish people supported the Treaty, he advised de Valera not to split Sinn Féin, even if he was defeated in the Dáil; however, this advice was ignored.

He supervised the provision of schools and churches to serve the new parishes created and viewed all his work from a spiritual angle and was considered a wise and prudent ruler.

[4] Two major commemorative events can be seen as the highlights of his episcopacy, namely the centenary of Catholic Emancipation in 1929 and the Eucharistic Congress of 1932.

Byrne had generally cordial relations with the governments of both W. T. Cosgrave and Éamon de Valera, advising them on the issues of divorce and the constitution respectively.

[5] While his pastorals from the 1920s and 1930s reveal some of the typical hierarchical concerns of the period, such as immodesty and evil literature, he was cautious in lending moral sanction to emergency legislation.