The single-vehicle collision happened at 4.20am on the Shanaway Road at Woodstock on the outskirts of Ennis.
The gold-coloured, 2001 Toyota Avensis was travelling from Ennis when the driver lost control and crossed the road before crashing into a stone pillar at the entrance to Woodstock View housing estate.
Tyre tracks could be seen crossing the roadway.
The three friends had attended the county U21 hurling final in Ennis on Saturday. An 18-year-old, understood to have been the front-seat passenger, was pronounced dead at the scene.
The driver and backseat passenger, aged 19 and 21, were rushed to University Hospital Limerick. Two of the young men were cousins.
Gardaí arrived within minutes of the alarm being raised. They were alerted to the collision by locals, who heard the impact. A doctor from ShannonDoc, the out-of-hours GP service, also responded to the incident, as did two units of the fire brigade, three ambulances, and a rapid-response advanced paramedic unit.
Fire crews had to cut one of the victims from the wreckage. Fire-service first-responders assisted paramedics with CPR, which they carried out on the injured men.
The road was closed to facilitate an examination by garda forensic collision investigators, while the fire service placed protective screens around the car to shield it from public view.
The collision occurred opposite the entrance to the Woodstock Hotel and the Woodstock Golf Club.
Superintendent John Galvin said: “The collision happened at around 4.20am and we would like to hear from anyone who might have seen the car in the area of Woodstock or Shanaway Road, or anywhere else before the collision.
“If anyone was going to, or coming home from, work or might have been returning from a night out and they were in the area at the time, we would ask them to contact us at Ennis garda station.”
Ennis garda station: 065-6848100; Garda confidential line: 1800 666 111