Hitchings was born in Hoquiam, Washington, in 1905, and grew up there, in Berkeley, California, San Diego, Bellingham, Washington, and Seattle. He graduated from Seattle's Franklin High School, where he was salutatorian, in 1923, and from there went to the University of Washington, from which he graduated with a degree in chemistry cum laude in 1927, after having been elected to Phi Beta Kappa as a junior the year before. That summer, he worked at the university's Puget Sound Biological Station at Friday Harbor on San Juan Island [1], and received a master's degree the next year for his thesis based on that work.

From the University of Washington, Hitchings went to Harvard University as a teaching fellow, ending up at Harvard Medical School. Before getting his Ph.D. in 1933, he joined Alpha Chi Sigma in 1929.

Following his PhD, he worked at Harvard and Case Western Reserve University. In 1942, he went to work for Wellcome Research Laboratories, where he began working with Gertrude Elion in 1944. Drugs Hitchings' team worked on included 2,6-diaminopurine (a compound to treat leukemia) and p-chlorophenoxy-2,4-diaminopyrimidine (a folic acid antagonist). According to his Nobel Prize autobiography,

In 1967 Hitchings became Vice President in Charge of Research of Burroughs-Wellcome. He became Scientist Emeritus in 1976. He also served as Adjunct Professor of Pharmacology and of Experimental Medicine from 1970 to 1985 at Duke University. Hitchings died in 1998 in Chapel Hill, North Carolina. Hitchings founded the Triangle Community Foundation in 1983. Hitchings is a member of the Medicinal Chemistry Hall of Fame. His wife died in 1985.

Hitchings was awarded the Passano award by the Passano Foundation in 1969, and the de Villiers award in 1970. He was elected a Foreign Member of the Royal Society (ForMemRS) in 1974.