Gardai were alerted to the incident at Ashfield Park at around 4 pm today.
Three people were rushed to hospital.
One man, aged in his 450s, was taken to James Connolly Memorial Hospital where he has since been pronounced deceased.
A second man (aged in his 20s) and a woman (20s) have both been taken to the Mater Hospital to be treated for serious injuries.
The scene has been preserved for a technical examination.
A garda spokeswoman said: “A post mortem of the deceased will take place tomorrow which will direct the further course of the investigation.
“An Garda Síochána are not looking for anyone else in relation to this incident at this time.
“Investigating Gardaí are appealing to speak with any person or any road users with camera footage (including dash cam) who may have been in the Ashfield Park area between 12 noon and 4pm on the afternoon of Monday 4th October 2021.
“Anyone with information is asked to contact Blanchardstown Garda station on 01 666 7000, the Garda Confidential Line on 1800 666 111 or any Garda station.”