In a statement on Monday, marathon organisers announced the death of John Allen and described him as a “deeply respected figure in the athletics community and a cornerstone of the Belfast City Marathon”.
It’s understood Mr Allen had been undergoing treatment for cancer over recent years.
Tens of thousands of people across Northern Ireland took part in the annual marathon on Sunday.
Mr Allen had been a director of the organisation for over four decades and served as chair for six.
In a statement the marathon organisers added: “John dedicated much of his life to the advancement of athletics in Northern Ireland.
“He was instrumental in shaping the Belfast City Marathon, serving as a Director since its inception in 1982, and more recently as chair for six impactful years.
“His vision, leadership, and passion for sport helped elevate the event into one of the most anticipated fixtures in the city’s calendar.
“Known not only for his remarkable technical contributions but also for his mentorship, John played a pivotal role in guiding the Marathon’s management team. His wisdom, warmth, and unwavering commitment left a lasting legacy that will continue to influence the event — and its people — for years to come.
“John will be remembered as a gentleman, a leader, and a tireless advocate for athletics. He will be deeply missed by his family, friends, colleagues, and the wider sporting community.”
Other tributes in the athletics community came from east Belfast running club Willowfield Temperance Harriers, who said Mr Allen had a 60 year association with the organisation.
“John has been associated with Willowfield for over 60 years,” they wrote.
“His many years of service into the club have been invaluable especially around the clubs race, the Seeley Cup, who without him the race wouldn’t be the success it is today.
“His wisdom and unwavering commitment to the athletics community in NI will always be remembered and he has left a lasting legacy that will continue for years to come.
John Allen, Chair of Belfast City Marathon
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“We know he will be greatly missed by everyone at Willowfield, his colleagues in Athletics NI, UK Athletics and at the Belfast Marathon.”
Alliance Party MLA Peter McReynolds added his own tribute, writing on social media: “I’m very sorry to see this. I was fortunate to have met John over the years.
“A huge loss but he’ll be fondly remembered and his hard work will live on with every event he helped shape.”