The man first came to garda attention at around 6.30pm on Sunday evening when emergency services were called to an address in the An Grianan housing estate in Killenaule.
The man, who was at the house with a number of other people, had suffered a significant injury to his arm and was taken to hospital for treatment.
Gardai said the man then left the hospital and was found walking on the M8 motorway near junction six at 12.30am on Monday.
Officers removed him from the road and took him to the Chapelfield estate in Urlingford, Co Kilkenny.
Gardai left the Chapelfield estate after the man was observed at the front door of a house.
At 1.49am, gardai received a report of a disturbance at a house in the Chapelfield estate.
Gardai and an ambulance responded, and the man was brought to St Luke’s Hospital in Kilkenny where he later died.
Gardai said the matter was referred to the GSOC as a matter of procedure.
Officers have also launched an appeal for information about the man’s death.
They are particularly interested in talking to anyone who was at the house with the man in the Killenaule.
They also want to hear from anyone who saw the man on the M8 between 12am and 12.45am on Monday morning and anyone who was in the Chapelfield estate between 1am and 3.30am.
