Irish Rail is to begin the tender process for up to 600 electric or battery-electric powered carriages over the next 10 years.
The company has said it is the largest and greenest fleet order in Irish public transport history.
The process is supported by the National Transport Authority (NTA).
Iarnród Éireann is seeking expressions of interest from global train manufacturers.
It said a 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.
Irish Rail added that 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.
A notice for the tender has been placed in the Official Journal of the European Union (OJEU).
The company said it is expected to "attract the interest of virtually every major global train manufacturer, such is its scale".
A train at Newbridge Station in Co Kildare | Image: RollingNews.ie"It will ensure customers on our rail network benefit from up-to-date facilities and technology, and that there are scale benefits in the competitive tendering for the NTA-funded investment."
The tender process is also providing for a possible first tranche of battery-electric hybrid trains.
However, the overall order will see the greater Dublin area total rail fleet, and up to 80% of all heavy rail journeys in Ireland, set for a potentially emissions-free future.
Chief executive of Iarnród Eireann, Jim Meade, said: "The commencement of the tender process for our new fleet is the first major step in the DART expansion project, which will revolutionise public transport in the greater Dublin area, providing an even more frequent and environmentally sustainable commuting option for new and existing communities.
"It will also provide greater capacity for Intercity and regional commuter services as carriages currently utilised in the greater Dublin area will become available for other services."
A recent Oireachtas Climate Action Committee report recommended that the public transport elements of 'Project Ireland 2040' be prioritised.
The committee called for the speedy delivery of public transport investment to encourage more people to choose sustainable modes and leave the car behind.
