The man, in his 40s, had come to the attention of Gardai.
The Garda Ombudsman has been notified after the death of a man in Offaly who had come to the attention of officers.
Members of the force were called to a disturbance on Patrick Street in Tullamore at around 4pm yesterday afternoon.
A man in his late 40s was treated at the scene and taken to Tullamore Hospital where he was later pronounced dead.
A post-mortem will now be carried out, with the results to determine the course of the investigation.