The 38-year-old man was based at Donnybrook station in Dublin but was not on duty at the time.
He was pronounced dead at the scene and taken to hospital in Nenagh where a postmortem will be carried out today.
His name was not being released until all his family had been notified. The Garda Press Office confirmed the Garda Ombudsman will investigate the circumstances that led to the man’s death.
The crash happened one mile from Roscrea on the main Dublin Road at 3.50pm.
The driver of the car the garda crashed into was also taken to hospital but her injuries are described as not life-threatening. She was the only person in her car.
The crash resulted in the main N7 road being closed throughout the evening.
Meanwhile, a 40-year-old man died when his motorcycle hit a car at Curraghline on the Headford Road, Galway, yesterday afternoon.
The victim died on the roadside. His body was taken to University Hospital Galway where a postmortem will be carried out.
Gardaí said the woman driving the car suffered minor injuries but was also taken to hospital.
The crash happened at 3pm and gardaí have appealed for witnesses to come forward and contact Mill Street Station at 091-538000.