Born in Cobble Hill, British Columbia,[3] Kelsey attended St. Margaret's School from 1928 to 1931 in the provincial capital, graduating at age 15.

[3] Encouraged by one of her professors, she "wrote to EMK Geiling, M.D., a noted researcher [who] was starting up a new pharmacology department at the University of Chicago, asking for a position doing graduate work".

[5][6] During Kelsey's second year, Geiling was retained by the FDA to research unusual deaths related to elixir sulfanilamide, a sulfonamide medicine.

At that time, there was no law available to prosecute those who sold poison as medicine, and Kelsey observed the need to work around incomplete regulation.

Her initial reason for doing this was that the testimonials supplied by Richardson-Merrell contained no scientific methodology, and she recognized their authors as having published suspicious articles in the past.

[11][7] In December 1960, Leslie Florence published a letter in the British Medical Journal connecting thalidomide to neurological symptoms.

[4][12] The unexpected neurological effects caused her to recall her earlier work on the mechanism of birth defects, so she also requested animal studies to demonstrate that the drug would not be harmful to the fetus.

Despite the fact that thalidomide was already widely used in Europe and elsewhere, Kelsey remained suspicious and scrutinized this data with concern and skepticism, sometimes asking her husband to check her conclusions.

[7] Kelsey's insistence that the drug should be fully tested prior to approval was vindicated in November 1961 when the births of deformed infants in Europe were linked to thalidomide ingestion by their mothers during pregnancy.

[9] In March 1962, after distributing "experimental" tablets to tens of thousands of patients without approval (causing 17 malformed births), Richardson-Merrell at last withdrew their FDA application.

"[17] Kelsey insisted that her assistants, Oyama Jiro and Lee Geismar, as well as her FDA superiors who backed her strong stance, deserved credit as well.

[14][15] Companies were required to demonstrate the efficacy of new drugs, report adverse reactions to the FDA, and request consent from patients participating in clinical studies.

This was precisely the opposite of the truth: most applications were automatically approved by reviewers ignoring the 60 day deadline, while Kelsey had carefully sent out data requests for over a year.

In 1995, when she was eighty-one, the FDA's Center for Drug Evaluation and Research created a special position for her, Deputy for Scientific and Medical Affairs in the Office of Compliance.