The Rail Procurement Agency has announced the Citywest Luas extension will open on 2 July.
The RPA says the 4km extension, part funded by property developers, will add two million passengers a year to the light rail network.
The link will add five new stops to the Red Line line, including a park and ride facility at Cheeverstown, and will terminate in Saggart.
A group of developers - Davy Hickey Properties, Harcourt Developments and Jim Mansfield's HSS - contributed 55% of the total cost of €150m.
It is the third addition to the Luas system following the Cherrywood extension and the opening of the Docklands line.
The RPA is awaiting a decision from An Bord Pleanála and a decision on Government funding concerning the future of the BXD project which would link up the Red and Green lines in Dublin city centre.