Esther McKeon (24) and her partner Simon Barker (29) were frantically driving from their home in Meath when they were forced to pull over.
Esther had gone into full labour and Simon was forced to deliver the baby on the outskirts of Dunboyne.
Little Sean Thomas was wrapped in jackets after his dad brought him into the world with just mobile phone contact from emergency personnel to help.
"We're still getting over it. It was just a big rush," Simon told the Herald.
"Esther was shaking, and I didn't want to cut the cord. I could feel his heartbeat and about five minutes later help arrived," said Simon.
"They were taken to the Rotunda because it was the nearest hospital, and thankfully everything is fine. We didn't even have time to think, it was unbelievable," he added.
Esther had been due to give birth in the Coombe. She had a check up last Thursday morning when she was told she was 3cm dilated.
"But they said she could go home and she might go into labour that night, which is exactly what happened," Simon explained. "At around 11pm her waters broke, and we had to drop our 19-month-old daughter Ava to Esther's mother in Dunboyne. And we didn't make it far out of there," he added.
Simon explained how Esther was in terrible pain and she knew the baby was coming. He rang the gardai for an escort, but in the end he was patched through to ambulance control.
"They were asking if Esther could not push until the ambulance got there, but the little fella was coming anyway," said Simon.
After Sean Thomas was born Simon wrapped him in jackets to keep him warm.
The proud father said that although he had been at the birth of the couple's other baby, Ava, he never had such a hands-on experience before.
Now the couple are settling into life with a new baby in the household.
"Esther and the baby are both doing well," Simon commented. "We've already had plenty of sleepless nights, but it's just a matter of getting into a routine."
While a representative from the Coombe said that they could not comment on individual cases, they confirmed that any mothers who are diagnosed as being in labour are not discharged from the hospital.