John Blashford Snell was educated at Victoria College and at the Royal Military Academy Sandhurst, then commissioned into the Royal Engineers.
Among his expeditions were the first descent of the Blue Nile, during which he invented white water rafting 'by accident' (in 1968); crossing of the Darién Gap (1971 to 1972) and overseeing the first north-south vehicular journey from Alaska to Cape Horn; and a complete navigation of the Congo River (in 1974 to 1975).
In 1969 he founded the Scientific Exploration Society. In 1978 he established Operation Drake, which later developed into Operation Raleigh, an educational initiative for young people, of which he was director general until he retired from this post in 1991.
In 2006 he helped the London hatmakers James Lock to design a hat especially to meet the needs of explorers.
His publications include an autobiography, Something Lost Behind the Ranges (1994).