'Blind Dave', as he prefers to be known, was inspired to attempt the feat after his own guide dog helped him regain his independence.
The charity has given him three dogs in the past 10 years: Peter, Carla and, currently, Wicksie. The first leg of the Seven Magnificent Marathons challenge will take place in Port Stanley on the Falkland Islands on 7 April.
Six legs will follow in Santiago in Chile, Los Angeles in the US, Sydney in Australia, Dubai, Nairobi in Kenya and in the Flora London Marathon on 13 April. Heeley will be accompanied by his sighted guide, Malcolm Carr, on his epic journey.