Emergency services were alerted shortly after 3pm after the young man was found in a small indoor section of the electricity plant.
It is believed the victim was a third-year apprentice and he was on a ladder at the extensive electricity installation when the tragedy occurred.
The 220,000 volts ESB facility covers a large site near the M50 and a large number of electricity pylons are situated in the vicinity.
At a separate location at the facility, construction work has been in progress.
Today, a construction worker at the site said: "All work stopped when it happened. We could see a lot of gardai, firemen and health people arriving. We heard he was on a ladder when it happened."
Several homes in parts of North Dublin lost electricity supplies for a period following the accident, including homes in the Donnycarmey area.
Paramedics tended to him at the scene before bringing him to the Mater Hospital were he was later pronounced dead.
The young man, from Santry, was an employee of ESB Networks.
Investigations are being carried out by the ESB and by the Health and Safety Authority.
It is understood early indications were that he had been electrocuted.
He had been working with three others at the time but there were no other injuries.