Clarkson's Farm's Charlie Ireland, known on the show as Cheerful Charlie, will be running 31 miles in the 31 days of January to raise money for the Motor Neurone Disease (MND) Association.
In a video on Instagram following his first run, Mr Ireland, an ambassador for the charity, said it had been surprisingly challenging.
Motor neurone disease
"Mile one down. I was going to sneak in a couple of extras but frankly I thought that was cheating on the first day.
"We wish you all the very best of luck and we'll keep you updated."
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MND is a fatal, rapidly progressing disease that affects the brain and spinal cord and affects people from all backgrounds.
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It attacks the nerves that control movement so muscles no longer work. MND does not usually affect the senses such as sight, sound and feeling etc.
It can leave people locked in a failing body, unable to move, talk and eventually breathe.
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MND kills a third of people within a year and more than half within two years of diagnosis.
It affects up to 5,000 adults in the UK at any one time and kills six people per day in the UK, just under 2,200 per year.
It has no cure.
More information about MND can be found at mndassociation.org
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