In 1948, Davidson joined the Foreign Office and served diplomatic posts in Washington, Brussels, Cairo, the Hague, and, from 1973 to 1975, ambassador to Laos. While living in Vientiane, the capital, his wife asked him to look for a cookbook on fish because she did not recognize any of the local varieties. Not being able to find one he wrote one himself together with an Italian ichthyologist who happened to be visiting. The original manuscript was copied with a stencil machine. A copy reached the British cooking guru Elizabeth David, who passed it on to Penguin, which published it in 1972 as Mediterranean Seafood. The book has since become a standard reference work, and is characterized by its creative mixture biology and recipes.
This was followed by Seafood Of South East Asia (1979) and North Atlantic Seafood (1979) for which he travelled throughout the region, gathering thousands of recipes from Portugal to Iceland.