“Grandfather Peng” was pronounced dead at 0.45am at Chombueng Crown Prince Hospital in Chom Bung district of Ratchaburi province.
The elderly runner left behind a 89-year-old wife, one son and four daughters.
Grandfather Peng started running about 30 years ago when he retired from rice farming at the age of 70.
He has long been a symbol of the famous Chom Bung Marathon, one of the major running events in Thailand.
There are four major marathons in Thailand - the Bangkok Marathon, the Khon Kaen Marathon, the Pattaya Marathon and the Chom Bung Marathon.
The self-trained runner completed his first full marathon run, covering a distance of 42.195 kilometres, in the annual event organised by the Chom Bung Rajabhat University when he was 72.
At the time, he ran in the 60-year-old or older category and was the oldest runner in the event which attracted more than 5,000 runners every year.
Grandfather Peng made the news headlines the following day after he passed the finish line before half of the participants half his age.
Since then, he was recognised as the oldest marathon runner in the country who could not find other runners his age to match him.
"I eat Thai traditional food which does not contain too much fat, and I don't smoke and drink alcohol, or even coffee," Grandfather Peng told a Bangkok Post reporter in 2008.
When the retired farmer was in his 80s, he competed in almost every running event around the country, and completed four full marathons. As he got older, he only ran in the 10K mini-marathon because it was too risky for him to participate in a full, or even a half-marathon.
His best time for the full marathon was four hours, 20 minutes.
Grandfather Peng won many medal and trophies. At the age of 94, he was still taking part in the Chom Bung 10K mini-marathon. He completed his last run in that race in 2012.