Councillor Russell B Hamilton has decided to resign as member for Pontrilas Ward, with effect from midnight on 1 October 2013.
A by election will be held and more information will be available in due course.
Councillor Tony Johnson, leader of Herefordshire Council, said: “On a professional and personal level, I would like to say how sad I am at Councillor Hamilton’s decision to leave the council.
“He is without doubt the hardest working councillor serving at present. I think it is unlikely that the people of Herefordshire will ever understand the difference he has made for them over the past few years.
“At a personal level he has been a great friend not just to me but to the officers with whom he has worked. His dedication and friendship will be missed.”