The woman died after she was struck by a van in Ballyshannon, Co Donegal.
The incident occurred on Main Street in the town at around 1.50am.
The woman was pronounced dead at the scene and her body was removed to the Shiel Hospital.
The driver of the van was uninjured.
The scene has been preserved for a technical examination and the road is closed.
Gardaí have appealed to anyone with information to contact Ballyshannon Garda Station on 071- 9858530 or the Garda Confidential Line 1800 666 111.
Last year, 196 people died on the roads in the Republic.
In Northern Ireland, 79 people – including children, pensioners, pedestrians and motor cyclists died in 2014, a huge jump on the previous year.
This was despite high profile police and DoE television advertising campaigns aimed at trying to stem the tide of road deaths.