During its first decade , the newly formed Irish Free State was governed by the victors of the civil war . When de Valera achieved power , he took advantage of the Statute of Westminster and political circumstances to build upon inroads to greater sovereignty made by the previous government . The oath was abolished and in 1937 a new constitution was adopted . This completed a process of gradual separation from the British Empire that governments had pursued since independence . However , it ain't until 1949 that the state was declared , officially , to be the Republic of Ireland .