Thousands of mourners are expected at the Mass of the Angels for two-year-old Kate and 12-week-old Grace Gilmore at the Church of the Sacred Heart in Belclare in north Co Galway.
Four years ago, their parents John and Michelle Newell were married in the same church as they set out on life together.
This morning, they will lead the mourners as their only children are laid to rest following the crash which cut short their lives while they were out on a Sunday afternoon stroll with their father.
They were killed when a car came onto the hard shoulder on the N17 in Tuam, Co Galway, a short distance from their home at The Meadows.
The girls were rushed to University Hospital Galway but were pronounced dead.
Gardaí have reissued their appeal for witnesses to the crash.
It is believed that the sole occupant of the Toyota Avensis car, who is also from Tuam, may have suffered a seizure behind the wheel before the crash. He was hospitalised after the accident for non-life threatening injuries.
The mayor of Co Galway, Cllr Tom Welby, said the deaths of the two little girls had shocked the nation.
“There has been grief and sadness since Sunday, not just in Tuam and Galway but throughout the country,” he said. “It is just such a terrible thing to happen. There has been such an outpouring of grief.”
Mr Welby and the mayor of Galway city, Cllr Terry O’Flaherty, opened a book of condolences at County Hall, which will remain open for the week.
Thousands of people queued to sign a book of condolences at Tuam Town Council yesterday, with the office remaining open late yesterday evening to facilitate the amount of people.
The Mass of the Angels will take place at 12pm at the Church of the Sacred Heart in Belclare, a short distance form Tuam, followed by burial in nearby Killower Cemetery.