The 2.5 million pounds profit came from his best-selling Christian books, artwork, calendars and cards. He was awarded an Order of the British Empire (OBE) in 2000 for his dedication.
Askew's daughters, Jenny Hawke and Stephanie Bell, asked mourners not to wear black because Askew, a talented painter, loved colour. Jenny said she and her sister were immensely proud of their father's achievements.
She told the media: "We've just learnt he'd sold his millionth book, which is an amazing achievement. He was faintly surprised by all the success. He just did what he did. He loved the written word and painting."
Askew and his wife began working with leprosy sufferers in India 57 years ago after being inspired by an exhibition about the disease. They boarded a ship to India in 1950 and ended up running one of the country's largest leprosy hospitals in West Bengal for 15 years.
Askew returned to England in 1965, following the birth of Jenny and Stephanie, and worked in London as international director for the Leprosy Mission for 13 years.
Leprosy Mission spokesman Tim Hunt said: "Eddie's amazing life gives us much for which to be thankful."