The DART+ West project will connect Maynooth, in County Kildare, with the M3 Parkway close to Dunboyne, in County Meath, starting in Connolly/Spencer Dock in north Dublin.
Many towns, including Maynooth, Leixlip, and Castleknock, will have access to a more environmentally friendly transit alternative thanks to the initiative, according to Iarnród Éireann.
The national railway operator stated that if the proposal was approved, building would begin in 2024 and the new service could begin running by
2029 when it submitted for the Railway Order in July 2022.
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 declared that it "warmly welcomes" An Bord Pleanála's judgement.
The proposal, according to the business, would treble the capacity of the Greater Dublin Area train network, and the order represents a "crucial milestone" for it.
An Bord Pleanála approved the Railway Order but with several restrictions, one of which was that the planned depot west of Maynooth could not be built because of the possibility of flooding.
Iarnród Éireann, however, stated that it will look at other ideas for building 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 stated that construction-related activities will immediately start.
"Iarnród Éireann will now move the DART+ West project delivery into its construction stage in cooperation with the National Transport Authority.
"This will involve procurement processes to engage contractors to undertake the construction activities on the scheme."