The collision involved a motorcycle and a car on the N81 at Poulaphouca
The incident occurred at around 3.30pm today.
The motorcyclist (a male and age unknown) was pronounced dead at the scene.
A second male motorcyclist has been taken to Tallaght University Hospital.
The driver of the car was uninjured.
Forensic Collision Investigators are at the scene. Diversions are in place and the road is expected to remain closed over the next number of hours.
Gardaí in Baltinglass are appealing for any witnesses, particularly any motorists with dash cam footage, to contact Baltinglass Garda Station on 059-6482610
or the Garda Confidential Line on 1800 666 111.