Originally a chartered surveyor in the family business, Dannatt was born in Blackheath, London. His artistic leanings were strong, and in the first instance related to music.

A self-taught painter, he was naturally energetic and eager to display his interpretations. His major geographical associations were with Dorset and Cornwall, where he concentrated his intense faculties on photography, geometric and abstract works. In retirement he lived with his wife in Wiltshire.