Born in Scotland, Sanderson traveled widely in his youth. His father, who manufactured whisky professionally, was killed by a rhinoceros while assisting a documentary film crew in Kenya in 1924. As a teenager, Sanderson attended Eton College, and, at 17 years old, began a yearlong trip around the world, focusing mostly on Asia. Sanderson earned a B.A. in zoology, with honors, fromCambridge University, where he later earned M.A. degrees in botany and geology. In a New York radio interview in March 1965 (WFMU's "Coffee Klatsch" hosted by Bob Zanotti), Sanderson stated that "I have three PhD's, but I don't call myself a doctor. Where I come from, that title is reserved for [medical] doctors". He did not elaborate as to the nature of these doctorates. In the 1930s, Sanderson led an expedition to Africa on behalf of the British Museum.
He became famous as the most credible witness to see a Kongamato, after being attacked by a creature he described as "the Granddaddy of all bats". This encounter occurred when he had shot a fruit batthat toppled into the water. He went to retrieve his catch but was warned by his partner to duck. He described the following events: "And I looked. Then I let out a shout also and instantly bobbed down under the water, because, coming straight at me only a few feet above the water was a black thing the size of an eagle. I had only a glimpse of its face, yet that was quite sufficient, for its lower jaw hung open and bore a semicircle of pointed white teeth set about their own width apart from each other. When I emerged, it was gone.
George was facing the other way blazing off his second barrel. I arrived dripping on my rock and we looked at each other. "Will it come back?" we chorused. And just before it became too dark to see, it came again, hurtling back down the river, its teeth chattering, the air "shss-shssing" as it was cleft by the great, black, dracula-like wings. We were both off-guard, my gun was unloaded, and the brute made straight for George. He ducked. The animal soared over him and was at once swallowed up in the night." The natives verified it as a Kongamato and ran for their lives, leaving their valuables behind.
Sanderson was an early follower of Charles Fort. Later he became known for writings on topics such as cryptozoology, a word Sanderson coined in the early 1940s, with special attention to the evidence for lake monsters, sea serpents, Mokèlé-mbèmbé, giant penguins, Yeti, and Sasquatch.
During the 1950s and 1960s, Sanderson was widely published in such journals of popular adventure as True, Sports Afield, and Argosy, as well as in the 1940s in general-interest publications such as theSaturday Evening Post. In the 1950s, Sanderson was a frequent guest on John Nebel's paranormal-themed radio program. He was a frequent guest on The Garry Moore Show, being one of the first recognized animal researchers on television to bring live specimens on talk shows. As his friend and fellow cryptozoologist Loren Coleman has remembered in several of Coleman's books, Sanderson's appearances often involved his discussion of cryptozoological topics.
