Named locally as 25-year-old Vincent Ryan, he was shot a number of times while sitting at a parked car in the Finglas area of Dublin this afternoon. He was rushed to the Mater Hospital but died later in the evening.
Mr. Ryan was the brother of Real IRA man Alan Ryan, who was murdered three years ago.
It is understood that Vincent Ryan was in the car alone at the time of the shooting, having just dropped his partner and a child at a nearby house.
Armed gardai are this evening patrolling the area as a precaution.