Massingham was the son of the journalist H. W. Massingham. He was brought up in London, and educated at Westminster School and Queen's College, Oxford. He failed to graduate from Oxford, because of bad health. He then became a journalist in London. He worked for the Morning Leader, Athenaeum, and the Nation, and knew D. H. Lawrence. In the 1920s he became a research assistant for two anthropologists from University College, London, and an interest in archeology and anthropology, which proved lifelong, led to the publication of Downland Man (1926) and a number of other works. He worked on a research project whose aim was to show that all megalithic culture in England had spread from Egypt.
By 1932 Massingham began to write more and more on country life, and the first of a long series of such books, possibly his best-known, was World Without End (1932), reflecting his experiences living in Chipping Campden in the Cotswolds. A serious accident happened in 1937, when he injured his leg, leading to a two-year period of regular hospital visits, at the end of which he hurt the same leg again, and it had to be amputated. He was forced to stop travelling as frequently as he had been doing and settled down to writing some thirty more books.
He was strongly influenced by the writings of Gilbert White and edited selections of White's writings. He was one of a group of ruralist British writers of the period; Massingham's friend Adrian Bell, a farmer in Suffolk, was another prominent writer, and John Musty suggests that Massingham may have had a hand in getting Bell published. They have attracted subsequent attention both as precursors to later developments, such as organic farming, and because of their political entanglements in the 1930s (for example, Henry Williamson was a supporter of Oswald Mosley). Massingham himself wrote in a vein compatible with the Social Credit and distributist ideas current at the time, as in his 1943 The Tree of Life.
He was one of the twelve members of the Kinship in Husbandry, set up in 1941 by Rolf Gardiner, a society dedicated to countryside revival in a post-war world. According to academics Richard Moore-Colyer and Philip Conford, Massingham was uncomfortable with what he felt was a pro-German tendency in this group. When the Kinship later merged with two other bodies to form the Soil Association, Massingham with Gardiner, the landowner Lord Portsmouth and the agricultural journalist Lawrence Easterbrook came onto the Soil Association's Council.