Having sketched birds as a child and learnt anatomy from taxidermy, Harrison went on to study at the Slade School and during this time made frequent trips to Scotland to observe Golden Eagles. This research led him to illustrate Seton Gordon's Days with the Golden Eagle. In 1938 Harrison went to Iceland to learn about ornithology and to study the landscape. He wrote and illustrated Bird Portraits and illustrated Jean Delacour's Pheasants of the World. Harrison then extended his study of birds, animals and landscapes into Africa. He lived Norfolk where he painted the rare birds of the Norfolk Broads and was a longtime supporter of the Norfolk Wildlife Trust.