The crash involving two cars happened at around 10.00 o clock on the N80 at Ballickmoyler.
A 48 year old woman who was driving one of the cars was pronounced dead at the scene.
The driver of the second car, a man in his 40s was taken to Tullamore Hospital where his injuries are described as serious.
The road is currently closed to traffic and local diversions are in place as Gardai carry out an examination of the scene.
Anyone who may have witnessed the crash is asked to contact Gardai.