Irish Rail is to begin the tender process for up to 600 electric or battery-electric powered carriages over the next 10 years.
Iarnród Éireann said it is the largest and greenest fleet order in Irish public transport history.
The company is seeking expressions of interest from global train manufacturers.
The process is supported by the National Transport Authority (NTA).
DART Expansion, electrification of lines to Maynooth, M3 Parkway, Hazelhatch and Drogheda, and key infrastructure works will allow more trains to operate in the greater Dublin Area.
The tender allows for the planned fleet expansion, replacement of the original DART fleet, and to ensure a framework is in place for more carriages to be ordered if there is further growth, the company said.
The overall order will see the rail fleet in the greater Dublin area, and up to 80% of all heavy rail journeys in Ireland, set for a potentially emissions-free future, as well as generating reductions in noise, and cost savings in train operations.
Iarnród Éireann said it is expected to "attract the interest of virtually every major global train manufacturer, such is its scale".
A notice for the tender has been placed in the Official Journal of the European Union (OJEU).