Buzyn, who specialises in hematology, cancer immunology and transplant, spent most of her career as a medical practitioner, professor and researcher at Paris Descartes University (Paris-V) and Necker–Enfants Malades Hospital.

Buzyn was born to two Holocaust survivors, her father Elie from Polish Łódź, who survived Buchenwald's death march at age 16, and left for British Palestine after World War II.

He became an orthopedic surgeon in Paris and married a French Jewish woman, Etty, whose family hid in France during the war; she became a well-known psychoanalyst and writer.

For several years she was a senior physician and researcher at the Necker Children's Hospital in Paris, teaching hematology and transplantation at Pierre and Marie Curie University (Paris-VI).

[7][8][9] She later steered through parliament a controversial bioethics law extending to homosexual and single women free access to fertility treatments such as in vitro fertilisation (IVF) under France's national health insurance; it was one of the campaign promises of President Macron and marked the first major social reform of his five-year term.

[12] Ahead of the 2019 European Parliament election in France, Buzyn was considered one of the front-runners to top the candidate list of the La République En Marche!

[13] By the end of 2019, addressing concerns that France's free health system was attracting illegal migrants, Buzyn said asylum seekers would have to wait three months before being entitled to healthcare.

[18][19] In January 2020, in the early stages of the COVID-19 pandemic, she caused controversy by calling temperature checks at airports "a symbol that is useless, except to please the population".