Gardaí said the man was discovered with serious injuries in Parnell Street at about 10.25pm on Friday.
He was taken to University Hospital Limerick but later died.
The Office of the State Pathologist has been informed and a post-mortem examination is due to take place on Saturday. There have been no arrests at this stage.
Police have appealed for anyone who was in the Parnell Street, Lord Edward Street and Davis Street areas on Friday, between 10pm and 10.40pm, and who has camera footage, to contact them.
