The National Union of Students-Union of Students in Ireland (NUS-USI) was established in 1972 under a unique arrangement where both the British and Irish national student unions, National Union of Students (NUS) and Union of Students in Ireland (USI) respectively, jointly organised in Northern Ireland to promote student unity across the sectarian divide.

The original agreement was revised in 2012. This resulted in the current trilateral agreement which was signed by the presidents of NUS, USI and NUS-USI at an event held at Parliament Buildings, Stormont in 2012 which took place to celebrate 40 years of collaboration between the national unions.