[11][12] As a Senior Scholar at St Hugh's College, Oxford,[13] she completed her DPhil degree in 1977 under the supervision of Anthony David Smith on the Origins of acetylcholinesterase in cerebrospinal fluid.

Greenfield has written several books about the brain, regularly gives public lectures, and appears on radio and television.

[15] Since 1976, Greenfield has published approximately 200 papers in peer-reviewed journals, including studies on brain mechanisms involved in addiction and reward,[16][17][18][19][20] relating to dopamine systems and other neurochemicals.

[21][22] She investigated the brain mechanisms underlying attention deficit hyperactivity disorder (ADHD)[22][23] as well as the impact of environmental enrichment.

[32] As a result of her recommendations,[citation needed] South Australian Premier Mike Rann made a major funding commitment, backed by the state and federal governments and the private sector, to establish the Royal Institution of Australia and the Australian Science Media Centre in Adelaide.

[38] Greenfield sits in the Parliament of the United Kingdom in the House of Lords as a crossbencher, having no formal political affiliation.

[42] In 2013, Greenfield published a dystopian science-fiction novel, 2121: A Tale from the Next Century, telling the story of videogame-playing hedonists and their conflict with "Neo-Puritans".

[48] She noted that Public Health England had related social networking and multiplayer online games to "lower levels of wellbeing", and believed that evidence pointed to a "dose response" relationship, "where each additional hour of viewing increases the likelihood of experiencing socio-emotional problems".

[49] She believed this raised questions about where to draw the boundaries between beneficial and harmful use of such technology, saying that "it would be surprising if many hours per day of screen activity did not influence this neuroplasticity".

In 2001, she became a Life Peer under the House of Lords Appointments Commission system,[58] as Baroness Greenfield, of Ot Moor, Oxfordshire.

[63] She is a founder and trustee of the charity Science for Humanity, a network of scientists, researchers and technologists that collaborates with not-for-profit organisations to create practical solutions to the everyday problems of developing communities.