Nestor was born in Franklin, New Jersey, and had nine siblings. He graduated from Georgetown University medical school in 1940. During World War II, he served in the United States Air Force as a flight surgeon and was awarded a Bronze Star for valor.
After the war, Nestor served as chief resident at Children's Hospital. While in private practice, he taught pediatrics at Georgetown and Howard University medical schools, as well as consulting with hospitals and government agencies. In 1961, Nestor joined the FDA.
During his employment at the FDA, Nestor revealed to the public that FDA leaders pressured reviewers, demanding new drugs be approved without adequate testing. He testified to Congress about the influence of pharmaceutical companies at the FDA and about FDA officials allowing drugs to stay on the market even after serious side effects had been identified. Despite receiving commendations from the Justice Department for uncovering fraudulent lab reports, Nestor was transferred from drug review duties by the FDA. Nestor fought the transfer and eventually resumed reviewing drugs.
On March 19, 1972, the FDA reassigned Nestor to its Office of Compliance, as part of a reorganization in which Civil Service doctors were replaced as drug approvers by consultants who were often affiliated with commercial companies. Nestor began a grievance proceeding. A review panel determined that senior FDA officials gave "misleading" testimony against Nestor and concluded that Nestor was due an apology and appropriate duties. In 1977, the FDA commissioner restored Nestor to the position he held before the 1972 transfer.
Robert G. Vaughn wrote in his book "The Successes and Failures of Whistleblower Laws" that Nestor "became one of the best-known FDA whistleblowers of all time."
Nestor also achieved fame in the Washington, D.C. area in 1984 after The Washington Post published his letter describing his favored driving method: On highways Nestor would settle his vehicle in the far left lane and set the cruise control at the speed limit, at the time 55 mph. He would not move to the right for drivers behind him. "Why," he asked, "should I inconvenience myself for someone who wants to speed?"  Nestor also believed he was performing a public service by forcing people to obey the nationwide 55 mile-per-hour speed limit. Nestor's letter enraged many motorists and led Paul J. Leonard to coin the term 'Nestoring' to describe the practice in another letter to the editor.
Nestor died of renal failure in 1999 at the age of 86 in Virginia, where he had lived for 50 years.
- "Physician John Nestor Dies". Washington Post. May 5, 1999. Retrieved April 14, 2019.
- Weil, Martin (May 5, 1999). "Physician John Nestor Dies; FDA Official Renowned for Strict Driving Habits". Washington Post. Archived from the original on October 22, 2012. Retrieved October 31, 2008.
- "John Nestor: Strife in the Fast Lane". Washington Post. November 21, 1984. Retrieved April 14, 2019.
- Vaughn, Robert G. (2021). The Successes and Failures of Whistleblower Laws. Edward Elgar Publishing. pp. iii–iv. ISBN 9781849808385.
- "Merrell Drug Sale Cited In Indictment of FDA". The Cincinnati Enquirer. March 21, 1963. p. 30.
- Greenberg, Daniel S. (September 6, 1977). "FDA head makes few internal changes". The Journal Herald (Dayton, Ohio). p. 20.
- Schmeck, Harold M. (April 3, 1972). "Nader Group Sees Pressure on F.d.a." The New York Times. Retrieved April 14, 2019.
- Roosevelt, Edith Kermit (May 21, 1972). "FDA's Effectiveness Impeded by Pressures". The Spokesman-Review (Spokane, Washington). p. 4.
- "FDA to Propose Reform of Nation's Drug Laws". The Town Talk (Alexandria, Louisiana). October 27, 1977. p. 39.
- Vaughn, Robert G. (2012). The Successes and Failures of Whistleblower Laws. Edward Elgar Publishing. p. ix. ISBN 9781849808385. Retrieved April 14, 2019.
- Kelly, John (October 24, 2008). "John Kelly's Washington". Washington Post. Retrieved October 31, 2008.
- Suplee, Curt (November 21, 1984). "John Nestor: Strife in the Fast Lane". The Washington Post.
- Davenport, John E. (November 10, 1984). "Letter to the Editor 6 -- No Title". Washington Post. Retrieved October 31, 2008.