Thousands of people around the country will take part in the 'Darkness into Light' fundraiser in the early hours of the morning.
Beginning at 4.15am the event will see participants run or walk across the line as dawn breaks.
The event is organised by suicide and self-harm prevention charity, Pieta House, with the fundraiser celebrating its eighth year.
Louise Quinn will be taking part in the event tomorrow and explains why she got involved:
She says that her daughter kept her going during her darkest periods: