She worked in the British Colonial Office until 1947, when she returned to Oxford to take up graduate study she had left. She studied with M. N. Srinivas as well as Edward Evans-Pritchard. In 1949 she did field work with the Lele people in what was then the Belgian Congo; this took her to village life in the region between the Kasai River and the Loange River, where the Lele lived on the edge of the previous Kuba kingdom.
In the early 1950s she completed her doctorate, married James Douglas and started a family of three children. She taught at University College, London, where she remained for around 25 years. She taught and wrote in the USA for 11 years. She published on such subjects as risk analysis and the environment, consumption and welfare economics, and food and ritual, all increasingly cited outside anthropology circles.
After four years (1977-81) as Foundation Research Professor of Cultural Studies at the Russell Sage Institute in New York, she moved to Northwestern University as Avalon Professor of the Humanities with a remit to link the studies of theology and anthropology. Her reputation was established by her book Purity and Danger (1966). She wrote The World of Goods (1978) with an econometrician, Baron Isherwood, which was considered a pioneering work on economic anthropology.
She became a Dame Commander of the Order of the British Empire in the Queen's New Year's Honours List, published on 30 December 2006. She died on 16 May 2007 in London, aged 86, from complications of cancer, survived by her three children. Her husband died in 2004.
In Purity and Danger, Douglas first proposed that the kosher laws were not, as many believed, either primitive health regulations or randomly chosen as tests of Jews' commitment to God. Instead, Douglas argued that the laws were about symbolic boundary-maintenance. Prohibited foods were those which did not seem to fall neatly into any category. For example, pigs' place in the natural order was ambiguous because they shared the cloven hoof of the ungulates, but did not chew cud.
Later in a 2002 preface to Purity and Danger, Douglas went on to retract her initial explanation of the kosher rules, saying that it had been "a major mistake." Instead, she proposed that "the dietary laws intricately model the body and the altar upon one another" as of land animals, Israelites were only allowed to eat animals which were also allowed to be sacrificed; these animals which depend on the herdsmen. Thus, Douglas concludes that the animals which are abominable to eat are not in fact impure, as the "rational, just, compassionate God of the Bible would [never] have been so inconsistent as to make abominable creatures."