Gardaí received reports last night of a “serious” one-car collision on the N60 between Ballyhaunis and Ballinlough.
The incident took place at Cloonafarna, near the border between Mayo and Roscommon shortly before 11pm.
A 19 year old man was pronounced dead at the scene, which was attended by gardaí, the fire service and ambulance service personnel.
Another man, aged 21, was taken to Mayo University Hospital where he is being treated. His injuries are not thought to be serious.
The road currently remains closed with diversions in place through Cloonfad from the Ballyhaunis side and also from Ballinlough.
The road is expected to remain closed over the morning while a forensic collision investigation is conducted.
The incident is being investigated by gardaí from Claremorris, who are appealing to anyone who travelled along the N60 between 10:30pm and 11.15pm last night to check for video footage and make it available to them.
Anyone with information is asked to contact gardaí in Claremorris or the Garda Confidential Line on 1800 666 111.