The 29-year-old from Kendal, who worked in Michelin-starred restaurants before becoming a private chef, had been running the race for the Lake District’s Brathay Trust charity in memory of his father who died 18 months ago.
Helen Hokin, who was Mr Campbell’s PR consultant, told the BBC: “He was a lovely, kind-hearted and down-to-earth man. I believe he was poised to become the next great innovator in British food.
“He was in the middle of a roadshow tour and he had such a way with inspiring young chefs. This is so sad.”
Mr Campbell (pictured) appeared on the BBC’s MasterChef: The Professionals in December 2017 and made it through to the semi-finals.
He began his career working in Michelin-starred restaurants after finishing second in the BBC’s Young Chef of the Year aged 20 in 2009.
According to his website he left the UK for the French Alps and cooked in private villas and “award-winning luxury” ski chalets.
“Combining my passions for cooking & travelling I spent the next 8 years expanding my culinary horizons as far and wide as possible,” he added.
A spokeswoman for MasterChef said: “We are shocked and saddened to hear the news about Matt Campbell, one of our talented contestants from last year.
“It was a privilege to have him on the show. He will always be remembered for producing some of the most innovative and groundbreaking food that we saw on the series.
“From the whole MasterChef team, our sincere condolences and thoughts are with his family and friends.”
Food writer and broadcaster Jay Rayner tweeted: “If you would like to do something in memory of chef Matt Campbell, who died running the marathon yesterday, his just giving page is here.
“He was raising funds for the Brathay trust, which works to improve the life chances of children and young people.”