Born at Dunkery, Park Road, Barnet on 17 August 1924, Wallis was the daughter of Leonard Francis Wallis (1880-1965) and Mary McCulloch Jones (1884-1957). She attended St Paul's Girls' School (1934–43) and studied geography at St Hugh's College, Oxford, where she completed her D.Phil degree in 1954.
In 1951, she was appointed assistant to R.A. Skelton, superintendent of the Map Room at the British Museum, succeeding him in 1967. She was the first woman to hold the post. In 1968 she was responsible for the acquisition of the map collection of the Royal United Services Institution. She also discovered the earliest version of England's first globe, by Emery Molyneux and thought to date from 1592, at Petworth House.
She was the chairman of the standing commission on the history of cartography of the International Cartographic Association. In 1986, she became president of the International Map Collectors' Society and she was a founder of The Geography and Map Section of the International Federation of Library Associations. She served as President of The Society for Nautical Research, 1972-1988, and President of the British Cartographic Society.
She died of cancer on 7 February 1995 at the Hospital of St John and St Elizabeth in St John's Wood, London.
Honours and awards
- Order of the British Empire, 1986
- Hon. D.Litt. Davidson College, North Carolina
- Honorary Fellow of Portsmouth Polytechnic
- Society Medal of the British Cartographic Society
- Caird Medal of the National Maritime Museum
- Victoria Medal of the Royal Geographical Society
- Honorary Fellow of the International Cartographic Association
- Honorary Fellow of the Library Association
- The Independent 14 February 1995, by W.R. Mead
- Wallis, Helen (1965). Carteret's voyage round the world, 1766-1769. Cambridge: Published for the Hakluyt Society at the University Press. pp. 2 v.
- Cartographical innovations : an international handbook of mapping terms to 1900. [Tring, Herts]: Published by Map Collector Publications in association with the International Cartographic Association. 1987. pp. xx, 353. ISBN 0906430046.
- Historians' guide to early British maps : a guide to the location of pre-1900 maps of the British Isles preserved in the United Kingdom and Ireland. London: Royal Historical Society. 1994. pp. ix, 465. ISBN 0861931416.
- "The British Cartographic Society: The Awards > The Society Medal". Retrieved 15 October 2013.
- "Medals and Awards Recipients 1970-2007" (PDF). Royal Geographical Society. Retrieved 2009-06-26.
- Wallis, Helen Margaret. "Oxford Dictionary of National Biography". Retrieved 15 October 2013.