 Treacy finally made his Ireland U21 debut on 20 August 2008, scoring in a 1–1 draw against Austria U21.On 11 August 2010, Treacy made his senior international début for the Republic of Ireland against Argentina, coming on as a substitute in the second half for Keith Fahey in the first international at the new Aviva Stadium in Dublin.On 24 May 2011, Treacy earned a starting place winning his third cap with an impressive display in the 2011 Nations Cup game against rivals Northern Ireland.