Blake, a 25-1 outsider to win, is a Goldsmiths College music graduate who was previously nominated for the Mercury for his self-titled debut album which he recorded at his home in New Cross, south east London.
Accepting his award, he said it was "amazing" to be in the running for an award with chart veteran David Bowie.
Asked what he would spend the money on, he said: "I'll make sure it goes to some good use".
He added: "This is the first award I've ever won apart from a tennis trophy which I won when I was about 12-years-old at my school and I'll hold them in equal esteem".
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John, who began running for Age UK back in the 1980s when he was aged 53, has raised an incredible amount since then - more than £40,000.