Irish Rail says several investigations are underway after a DART train derailed north of Dun Laoghaire.
The company says the train experienced "a low speed derailment" at around 6:15pm.
There is no report of injuries to anyone onboard.
Customers onboard were walked back to the nearest station by Iarnród Éireann staff.
Irish Rail, the Rail Accident Investigation Unit and the Commission for Rail Regulation are all investigating the incident.
Some services were suspended for a time between Lansdowne Road and Dun Laoghaire.
A full service is expected to operate from first service in the morning.
Additional reporting: Jack Quann