Feilding is the youngest child of Basil Feilding, great-grandson of the 7th Earl of Denbigh and the Marquess of Bath, and his wife and cousin, Margaret Feilding. The Feilding family is descended from the House of Habsburg and came to England in the 14th Century. (Despite almost certainly being of Warwickshire origin, in the middle of the seventeenth century following their elevation to the aristocracy, the Feilding family began to claim descent from the Habsburgs through the counts of Laufenburg and Rheinfelden. The claim, though widely accepted at one time, including by the Historian Edward Gibbon, was also the subject of ridicule. It was comprehensively debunked at the start of the twentieth century. (J H Round (1901). Studies in Peerage and Family History. p. 216.)) Since then the family intermarried into the British aristocracy and is directly descended from two illegitimate</ref> children of Charles II of England and his mistresses Barbara Villiers and Moll Davis. She grew up at Beckley Park, a Tudor hunting lodge with three towers and three moats situated on the edge of a fen outside Oxford.
In 1966 Feilding met and formed a relationship with Dutch scientist Bart Huges. From the late 60s she lived with Joseph Mellen with whom she had two sons, Rock Basil Hugo Feilding Mellen (born 1979) and Cosmo Birdie Feilding Mellen (born 1985).
Feilding gained notoriety in 1970 when she performed trepanation on herself, about which she made a short cult art film entitled Heartbeat in the Brain. Trepanation was part of her exploration into the effects of different techniques to alter and enhance consciousness. During this period, she wrote Blood and Consciousness, which hypothesized that changing ratios of blood and cerebrospinal fluid underlie changes in consciousness, and also described the theory of the "ego" as a conditioned reflex mechanism that controls the distribution of blood in the brain. During the 1970s and 80s she painted and produced conceptual artworks associated with consciousness, which were exhibited at the ICA in London, PS1 in New York and other galleries in the US.
She and Mellen separated in the mid 1990s and on 29 January 1995 she married James Charteris, 13th Earl of Wemyss and March (then known by the courtesy title of Lord Neidpath), under the Bent Pyramid in Egypt. Feilding also uses the title Lady Neidpath. The family home is Stanway House in Gloucestershire.
Feilding has also been active in drug policy reform and was among the first to start building an evidence-base upon which new policies could be formed, arguing that benefits as well as harms should be considered. In 2007, Feilding convened the Global Cannabis Commission, producing a report authored by a group of leading drug policy analysts, which lays out a plan for possible reforms of cannabis control policies at national and international levels. 2011 saw Feilding bring together members of the Global Commission on Drug Policy Reform (a panel of world Leaders and intellectuals) and political Leaders from 14 countries interested in reform. Together, at the House of Lords, they launched the Beckley Foundation Global Initiative for Drug Policy Reform, a joint initiative with the All Party Parliamentary Group on Drug Policy Reform, which was set up to support the BF's initiative to drive forward alternative approaches to drug control to create more humane, evidence-based policies that would reduce the potential harm of drugs to individuals and societies.
From these meetings, two important reports were written and published. The first, in 2012, was entitled 'Roadmaps to Reforming the UN Drug Conventions'. It detailed ways in which the UN drug conventions could be amended to give countries greater freedom to adopt policies better suited to their individual needs. The next, in 2013, was a rigorous academic analysis by the widely respected Institute for Social and Economic Research. It discussed the possible outcomes of decriminalising and regulating cannabis in England and Wales. Also in 2013, President Otto Perez Molina of Guatemala asked Feilding to advise on the Guatemala government's policy on drugs, and in 2015, Mark Golding, the Jamaican Minister of Justice, invited Feilding to advise him and the government in developing plans for the country's new system of cannabis regulation. In May 2016, in response to the enforcement of the Home Office's Psychoactive Substance Act, the Beckley Foundation published a chapter on the regulation of new psychoactive substances (NPS) from an upcoming report entitled Roadmaps to Regulation: Cannabis, Psychedelics, MDMA and NPS.
