Pauline Gregg Meiggs was born in north London to a working-class family. As a young woman, she was attracted to socialism through the writings of William Morris and joined the Labour League of Youth. Later she became a member of the Independent Labour party, and addressed the public from a soapbox at Speaker's Corner in Hyde Park. She got a job as a secretary at the publishing firm Longman before winning a place at the London School of Economics. She earned a doctoral degree with a dissertation on the Levellers leader John Lilburne, later the basis of her1961 biography Free-Born John. At the start of World War II, she worked at the Ministry of Supply, which posted her to Warwick. There she met historian Russell Meiggs, then a classics fellow at Balliol College, Oxford. They married in 1941 and settled into an Oxford academic life, with J.R.R. Tolkien among their wide circle of friends. She continued her research on the 17th century and began publishing under her birth name Pauline Gregg. Her first and most successful book, A Social and Economic History of Britain, 1760-1950 (1950), became a standard reference work. She also wrote acclaimed biographies of King Charles I (1981) and Oliver Cromwell (1988).