Emergency services responded to the incident at Patrician Park on Kill Avenue shortly after 8.30am on Sunday. Gardaí have preserved the area as a crime scene while technical and forensic examinations continue.
A post-mortem examination is expected to take place, and the Coroner has been notified of the man's death.
An investigation is now underway, with a senior investigating officer overseeing the case from an incident room established at Dún Laoghaire Garda Station.
Road closures remain in place on Kill Avenue and Glenageary Road Upper, with local traffic being diverted. Dublin Bus has also warned commuters that the E2 route between Dún Laoghaire and Harristown may experience delays.
As part of the investigation, Gardaí are conducting door-to-door enquiries and are asking witnesses to assist with their enquiries.
Drivers who were in the vicinity of Kill Avenue between 8am and 9am, particularly those with dash-cam recordings or other camera footage, are encouraged to provide it to investigators.
Anyone with relevant information is urged to contact Dún Laoghaire Garda Station on 01 666 5000, the Garda Confidential Line on 1800 666 111, or their nearest Garda station.
