The 1923 deportation of two Irish republican envoys was a signal moment in the construction of Australian immigration policy, remembered more in legal than political history. The arrival of the Irish envoys, anti-treaty, anti-Free State and anti-British, provoked anxieties about imperial loyalty and domestic harmony. This article contextualises the role of the envoys as a performance of Irish republican politics in the dying stages of the Irish Civil War before analysing the responses to them by Australian governments determined to curb their activities. Immigration policy and administration were constructed in this episode as an element of national security, one that implied a consideration for relations between states of a changing empire as well as the need for domestic harmony within Australian borders.