Helen Maud Cam was born in Abingdon, England, one of nine children of the Rev. William Herbert Cam, headmaster of Abingdon School, and his wife Kate. She was home schooled by her parents, then studied at Royal Holloway College in London, where she earned a First in History. She went on to obtain a master's degree in Anglo-Saxon and Frankish studies at the University of London. In 1908-1909, she received a fellowship in history at Bryn Mawr College, Pennsylvania, then returned to the UK and taught at Cheltenham Ladies' College. Prof. Cam’s focus throughout her career was on local government during the Middle Ages, and she was an innovator in her use of local sources for her research. Her first book, Local Government in Francia and England, 768–1034, was published in 1912. In 1921, she became a fellow of Girton College, Cambridge. She published The Hundred and The Hundred Rolls: An Outline of Local Government in Medieval England in 1930. In 1948, she became the first female professor at Harvard University when she was appointed to the Zemurray Radcliffe Chair in History, a position she held until her retirement in 1954. Other major works included England Before Elizabeth (1950) and Law Finders and Law Makers in Medieval England (1963). She also enjoyed historical fiction, and wrote a book on the genre, Historical Novels (1961). She was elected to the British Academy in 1945 and a Fellow of the American Academy of Arts and Sciences in 1950. In 1957 she was appointed CBE.