The India-origin runner, who is turning 102 on April 1, had recently announced his retirement after participating in the Hong Kong marathon.
He said that he has decided to give up marathon because of health reasons but will continue to run for charity works.
"I have quit marathons but I will continue to run. Running is my addiction and I am alive because of this activity," Singh said at a press conference here today.
"I am growing old and losing weight," he said, giving reasons why he decided to quit.
More From This Section
Singh, who was a farmer in Punjab before settling in England, has competed in nine 26-mile marathons in London, Toronto and New York.
He said that during his last race in Honk Kong, he was hurt after a nasty fall but that did not stop him from breaking his previous record in 10 km marathon.
He rubbished reports that he had challenged Indian Prime Minister Manmohan Singh to run with him, saying that he had never said like that.
"Indian PM is different person. I regard him as one of the finest brains in the world. For me it will be even privilege to see him," he said.
Answering to a query on how he kept his body fit, Singh said the key was to be happy and have a positive frame of mind.
"You can have the best food but if you are not happy then you cannot do anything. One needs positivity, happy mind and determination to win over challenges," he said.