The victim, aged in his 20s, fell before the 145 Dublin Bus service at the junction of Nassau St and Dawson St in the city centre at approximately 5.45pm.
The driver, who was unable to stop in time to avoid the man, was left extremely shocked by the incident.
The victim received horrific injuries and was declared dead at the scene.
Shortly after the incident it emerged that the victim may have been in a row with at least one other individual just before he fell to his death.
Gardaí confirmed they were investigating a “suspicious death” and appealed for any witnesses to contact them.
There were many people in the area at the time as it was rush hour. Witnesses were left traumatised by what happened.
Gardaí will also study onboard footage from the bus’s security camera to see if that sheds any light on the seconds leading up to the incident.
The body of the man remained at the scene last night and several roads around the area were closed off.
Dublin Bus, which is carrying out its own investigation into the incident, confirmed its vehicle was en route to Heuston Station.
* Gardaí asked witnesses or anyone with information to contact Pearse St Garda Station on 01 6669000, the Garda confidential line on 1800 666111, or any Garda station.