Aoife McGivney, a nurse at the Mater Hospital in Dublin, was running late for work yesterday morning when she boarded the number 16 bus in Ballinteer.
She was sitting downstairs at around 8am when the bus started rolling forward on O'Connell Bridge.
Speaking on RTÉ's Ryan Tubridy Show, Ms McGivney described the scene saying people were screaming and she could hear car horns as the bus went through a red light and hit a bike.
Ms McGivney said she realised the bus driver was unconscious after she saw him making jerking movements and he was not breathing properly.
"In that situation, there was no one else, it was like 'Oh My God' this is it."
She said three possible scenarios ran through her head.
Firstly, that the driver had had a seizure, but she also wondered if he had suffered a stroke.
She said: "But he had weakness on both sides, so that kind of ruled that one out and he wasn't talking ... he just wasn't conscious at all.
"So the last one then was that he was pre-arrest in that there was a heart attack there, which I believe is the cause of what happened."
Ms McGivney said she was able to reach in through the driver's door inside the bus, pull the window down and shake his legs to make sure they weren't on the pedals, before the bus eventually cut out and came to a stop.
She said the passengers managed to get the driver off the bus before putting him in the recovery position with her coat under his head and monitored his breathing and heart rate.
However, she said she soon noticed his heart and breathing both stopped and she started to administer CPR and told people to call an ambulance.
Ms McGivney said other people with training also stepped forward and shared CPR administration with her.
She praised the ambulance service for arriving quickly and said that with the help of Dublin Fire Brigade they were able to revive the driver.
A garda told her the man was conscious by the time he got to the hospital yesterday morning.
Ryan's chatting to heroic nurse Aoife McGivney who saved the life of a bus driver who suffered a heart attack while driving through rush-hour traffic in Dublin yesterday @RTERadio1 #DublinBus #CPR pic.twitter.com/3tnWvx9R98— Ryan Tubridy Show (@RyanTubridyShow) March 5, 2019
She said she hopes to go to visit him in hospital today.
"I don't know if he'll want to see me or anything but, for me, I need to see him alive, we're just so lucky. It was a very, very scary situation to be in," she said.
Ms McGivney said that even if someone did have first aid training, it is so hard to know when in that type of situation to start administering CPR.
She said that is the main reason she wants to talk about what happened because she wants to promote and talk about how important it is to get CPR training and to be able to actively recognise when someone is that unwell and when it is time to intervene.
She praised doctors and healthcare staff who provided her with the training to do what she did yesterday and said she is lucky to have had that training.
Ms McGivney said: "This was just one lucky moment that I got to be there and do this for him.
"I know most people in this profession would step up in a situation like this but I'm just very thankful that he's alive.
"Its very touching knowing that he's doing well. Hopefully he'll have many more years to come."
This evening, Lord Mayor of Dublin Nial Ring said he would nominate Ms McGivney for a National Bravery Award.
He said: "These are given to people from all walks of life and all sections of society who carried out a deed of bravery with 'an effort to save human life involving personal risk'. Aoife certainly fits that criteria."