An Bord Pleanála has given permission for the extension of the DART network to Kildare and Meath.
The DART+ West project will run from Connolly/Spencer Dock in north Dublin to Maynooth in Co Kildare and on to the M3 Parkway near Dunboyne in Co Meath.
The project will deliver a more sustainable transport option for a number of communities, such as Maynooth, Leixlip and Castleknock, Iarnród Éireann said.
When it applied for the Railway Order in July 2022, the national railway operator said if the project got the green light that construction would commence in 2024 and the new service could start operating by 2029.
The application from Iarnród Éireann included plans for a new station at Spencer Dock, to interchange with the Luas Red Line, a new second station entrance on Preston Street and rail capacity enhancements at Connolly Station.
It also proposed building a new DART depot west of Maynooth train station, to maintain the new DART+ fleet.
Iarnród Éireann said it "warmly welcomes" the decision by An Bord Pleanála.
It said the order is a "crucial milestone" for the plan which the company says will double the capacity of the Greater Dublin Area rail network.
In its decision An Bord Pleanála granted the Railway Order with a number of conditions including that the proposed depot west of Maynooth not be constructed due to concerns about flood risk.
However Iarnród Éireann said it will explore other options for the construction of a depot.
"We will immediately consider the requirements to progress this, to deliver the depot in line with the timelines to support the wider DART+ Programme."
It said work to get construction underway will now commence
"Iarnród Éireann, in collaboration with the National Transport Authority, will now progress the delivery of the DART+ West project into its construction stage.
"This will involve procurement processes to engage contractors to undertake the construction activities on the scheme."
