The Castlerea to Williamstown road will open later Friday morning following a fatal overnight crash.
The single-vehicle crash happened at around 2.20am on the R361 around a kilometre outside Williamstown.
The 19 year old male driver of the car was seriously injured, and was pronounced dead at the scene.
His body has been removed to the morgue at University Hospital Galway.
A forensic examination is being carried out at the scene of the crash, and the road remains closed with diversions in place.
Gardaí are calling for witnesses – in particular anyone who was on the stretch of road between 1.45am and 2.10am – to contact Tuam Garda Station on 093-708-40, the Garda Confidential Line on 1800-666-111 or any Garda station.