Condolences have been sent to all his family and friends by the WRU and he has been praised for his “incredible” service to the national sport of Wales.
The former school head teacher from Abergavenny represented District A on the WRU from 1993 and also served as vice-chairman until he chose to step down for health reasons earlier this year.
He has represented the WRU on the Board of the European Rugby Cup Ltd, the International Rugby Board and the Welsh Youth Rugby Union. He was a member of the Millennium Stadium Board and on the WRU Appointments and Remuneration Committee.
He played youth and senior rugby for Cwmtillery and Abertillery before joining Abergavenny where he coached for 20 years and was also honorary secretary of the then Monmouthshire League.
WRU chairman Gareth Davies said: “Ken represented the traditional values of this great game and on behalf of my fellow Directors and all of us at the Welsh Rugby Union I send sincere heartfelt condolences to Ken’s family and many friends, as they come to terms with their sad loss.
“Ken served the WRU with great distinction for over 20 years and, for more than a decade, he held the position of vice-chairman of the Welsh Rugby Union, a role he discharged with great diplomacy and pride.
“His reputation as a man of strong values who always sought to do his best for the game was known far beyond the borders of Wales.”
WRU president Dennis Gethin said: “Welsh rugby has lost a great administrator with the passing of Ken Hewitt and I have lost a true friend.
“My condolences go to all his family and friends at this very sad time as we reflect on the incredible contribution he made to our game.
“He saw our game through the introduction of professionalism and he was a Board director during the building of the Millennium Stadium.
“He will long be remembered as an important administrator who contributed a great deal to the well-being of our game.”