James Dewey Watson (born April 6, 1928) is an American molecular biologist, best known as one of the two co-discoverers of the structure of DNA, with Francis Crick, in 1953. Watson, Francis Crick, and Maurice Wilkins were awarded the 1962 Nobel Prize in Physiology or Medicine "for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material". He studied at the University of Chicago and Indiana University and subsequently worked at the University of Cambridge's Cavendish Laboratory in England where he first met his future collaborator and personal friend Francis Crick.

In 1956, Watson became a junior member of Harvard University's Biological Laboratories until 1976, promoting research in molecular biology and from 1968 he served as director of Cold Spring Harbor Laboratory (CSHL) on Long Island, New York, greatly expanding its level of funding and research. At CSHL, he shifted his research emphasis to the study of cancer. In 1994, he became its president for ten years, and then subsequently he served as its chancellor until 2007, when he resigned, partially due to a controversy over comments he made about race and intelligence during an interview with a trusted friend that made it into the press. Between 1988 and 1992, Watson was associated with the National Institutes of Health, helping to establish the Human Genome Project. Watson has written many science books, including the seminal textbook The Molecular Biology of the Gene (1965) and his bestselling book The Double Helix (1968) about the DNA structure discovery.

His father was of Scottish descent (both Dewey and Watson being Scottish surnames). His mother's father Lauchlin Mitchell, a tailor, was from Glasgow, Scotland, and her mother, Lizzie Gleason, was the child of Irish parents from Tipperary. Watson was fascinated with bird watching, a hobby he shared with his father. Thanks to the liberal policy of University president Robert Hutchins, he enrolled at the University of Chicago at the age of 15. After reading Erwin Schrödinger's book What Is Life? in 1946, Watson changed his professional ambitions from the study of ornithology to genetics. Watson earned his B.S. degree in Zoology from the University of Chicago in 1947. In his autobiography, Avoid Boring People, Watson describes the University of Chicago as an idyllic academic institution where he was instilled with the capacity for critical thought and an ethical compulsion not to suffer fools who impeded his search for truth, in contrast to his description of later experiences. Watson attended Indiana University from 1947 to 1950 as a graduate student. He received his Ph.D. from IU in 1950.

Watson was attracted to the work of Salvador Luria. Luria eventually shared a Nobel Prize for his work on the Luria-Delbrück experiment, which concerned the nature of genetic mutations. Luria was part of a distributed group of researchers who were making use of the viruses that infect bacteria, called bacteriophages. Luria and Max Delbrück were among the leaders of this new "Phage Group," an important movement of geneticists from experimental systems such as Drosophila towards microbial genetics. Early in 1948, Watson began his Ph.D. research in Luria's laboratory at Indiana University, and that spring he got to meet Delbrück in Luria's apartment and again that summer during Watson's first trip to the Cold Spring Harbor Laboratory (CSHL). The Phage Group was the intellectual medium within which Watson became a working scientist. Importantly, the members of the Phage Group had a sense that they were on the path to discovering the physical nature of the gene. In 1949 Watson took a course with Felix Haurowitz that included the conventional view of that time: that proteins were genes and able to replicate themselves. The other major molecular component of chromosomes, DNA, was thought by many to be a "stupid tetranucleotide", serving only a structural role to support the proteins. However, even at this early time, Watson, under the influence of the Phage Group, was aware of the Avery-MacLeod-McCarty experiment, which suggested that DNA was the genetic molecule. Watson's research project involved using X-rays to inactivate bacterial viruses. He gained his Ph.D. in Zoology at Indiana University in 1950 (at age 22).

Watson then went to Copenhagen University in September 1950 for a year of postdoctoral research, first heading to the laboratory of biochemist Herman Kalckar. Kalckar was interested in the enzymatic synthesis of nucleic acids, and he wanted to use phages as an experimental system. Watson, however, wanted to explore the structure of DNA, and his interests did not coincide with Kalckar's. After working part of the year with Kalckar, Watson spent the remainder of his time in Copenhagen conducting experiments with microbial physiologist Ole Maaloe, then a member of the Phage Group. The experiments, which Watson had learned of during the previous summer's Cold Spring Harbor phage conference, included the use of radioactive phosphate as a tracer to determine which molecular components of phage particles actually infect the target bacteria during viral infection. The intention was to determine whether protein or DNA was the genetic material, but upon consultation with Max Delbrück, they determined that their results were inconclusive and could not specifically identify the newly labeled molecules as DNA. Watson never developed a constructive interaction with Kalckar, but he did accompany Kalckar to a meeting in Italy where Watson saw Maurice Wilkins talk about his X-ray diffraction data for DNA. Watson was now certain that DNA had a definite molecular structure that could be elucidated.

In 1951, the chemist Linus Pauling in California published his model of the amino acid alpha helix, a result that grew out of Pauling's efforts in X-ray crystallography and molecular model building. Watson found out about Pauling's model quickly because it was communicated to him via Pauling's son, Peter Pauling, who had a copy of the manuscript. Watson claimed that such a model (with three central phosphate chains held together by hydrogen bonds) was easily recognized as incorrect because in an aqueous environment the phosphate groups would be ionized thus would not display hydrogen bonding and would repel each other. After obtaining some results from his phage and other experimental research conducted at Indiana University, Statens serum institute (Denmark), Cold Spring Harbor Laboratory, and the California Institute of Technology, Watson now had the desire to learn to perform X-ray diffraction experiments so that he could work to determine the structure of DNA. That summer, Luria met John Kendrew, and he arranged for a new postdoctoral research project for Watson in England.

Watson and Crick proceeded to deduce the double helix structure of DNA. Sir Lawrence Bragg, the director of the Cavendish Laboratory, where Watson and Crick worked, made the original announcement of the discovery at a Solvay conference on proteins in Belgium on April 8, 1953, which went unreported by the press. Watson and Crick submitted a paper to the scientific journal Nature, which was published on April 25, 1953. This has been described by some other biologists and Nobel laureates as the most important scientific discovery of the 20th century. Bragg gave a talk at the Guys Hospital Medical School in London on Thursday, May 14, 1953, which resulted in an article by Ritchie Calder in the newspaper The News Chronicle of London, on Friday, May 15, 1953, entitled "Why You Are You. Nearer Secret of Life." The news reached readers of The New York Times the next day. Victor K. McElheny, in researching his biography, "Watson and DNA: Making a Scientific Revolution", found a clipping of a six-paragraph New York Times article written from London and dated May 16, 1953, with the headline "Form of 'Life Unit' in Cell Is Scanned." The article ran in an early edition and was then pulled to make space for news deemed more important. The Cambridge University undergraduate newspaper Varsity also ran its own short article on the discovery on Saturday, May 30, 1953. Watson subsequently presented a paper on the double helical structure of DNA at the 18th Cold Spring Harbor Symposium on Viruses in early June 1953, six weeks after the publication of the Watson & Crick paper in Nature. Many at the meeting had not yet heard of the discovery. The 1953 Cold Harbor Symposium was the first opportunity for many to see the model of the DNA Double Helix. Watson claimed that he was refused a $1,000 raise in salary after winning the Nobel Prize. Watson, Crick, and Wilkins were awarded the Nobel Prize in Physiology or Medicine in 1962 for their research on the structure of nucleic acids.

At Harvard University, starting in 1956, Watson achieved a series of academic promotions from Assistant Professor, to Associate Professor to full Professor of Biology. He championed a switch in focus for the school from classical biology to molecular biology, stating that disciplines such as ecology, developmental biology, taxonomy, physiology, etc. had stagnated and could only progress once the underlying disciplines of molecular biology and biochemistry had elucidated their underpinnings, going so far as to discourage their study by students. He left the school in 1976.

In 1968, Watson became the Director of the Cold Spring Harbor Laboratory. Between 1970 and 1972, the Watsons' two sons were born, and by 1974 the young family made Cold Springs Harbor their permanent residence. Watson served as the Laboratory's Director and president for about 35 years, and later he assumed the role of Chancellor. In October 2007, Watson resigned as a result of controversial remarks not about race but about animals made to the press. Watson has one son who has schizophrenia. In October, 2007, Watson was suspended following criticism of views on race and intelligence attributed to him, and a week later, on the 25th, he retired at the age of 79 from Cold Spring Harbor Laboratory from what the lab called "nearly 40 years of distinguished service". In a statement, Watson attributed his retirement to his age, and circumstances that he could never have anticipated or desired.

In January 2007, Watson accepted the invitation of Leonor Beleza, president of the Champalimaud Foundation, to become the head of the foundation's scientific council, an advisory organ. He will be in charge of selecting the remaining council members. Watson was also a former advisor for the Allen Institute for Brain Science. .

In 1968, Watson wrote The Double Helix, one of the Modern Library's 100 best non-fiction books. The account is the sometimes painful story of not only the discovery of the structure of DNA, but the personalities, conflicts and controversy surrounding their work. Watson's original title was to have been "Honest Jim," in that the book recounts the discovery of the double helix from his point of view and included many of his private emotional impressions at the time. In the same way, Watson's first textbook, The Molecular Biology of the Gene, set a new standard for textbooks, particularly through the use of concept heads—brief declarative subheadings. Its style has been emulated by almost all successive textbooks. His next great success was Molecular Biology of the Cell, although here his role was more that of coordinator of an outstanding group of scientist-writers. His third textbook was Recombinant DNA, which used the ways in which genetic engineering has brought much new information about how organisms function.