The reigning national cross country champion set his PB in Scotland last week.
Cormac Dalton has become just the second man in the history of the Mullingar Harriers to run a sub four minute mile.
Dalton clocked a time of 3.59.51 at the Monument Mile Classic in Stirling, Scotland.
The national cross country champion joins just Mark Christie on a very exclusive club list.
The Mullingar runner has also represented Ireland this season at the European Cross Country Championships, and in the European Championship 10,000m on track.