The Cabinet has approved a preliminary business case from the National Transport Authority to lodge a planning application for MetroLink with An Bord Pleanála in September.
The project, which has been provisionally costed at over €9.5bn, would represent the largest rail infrastructure investment in the country since the turn of the century.
The plans would see MetroLink consist of a fully segregated railway, most of which will be underground from north of Swords to Charlemont in Dublin city.
It would serve Dublin Airport as well as Ballymun and Glasnevin.
Construction is set to begin in 2025 and be completed between 2031 and 2034.
The Cabinet heard that precise costs are too early to finalise, but that are credible estimated stress-tested costs put the final figure at over €9.5 billion.
