Gillett was born on Decemeber 12, 1883, Penn Yan, New York, the only child of Edward Chauncey Gillett and Mary Elizabeth (Doolittle) Gillett. The families of both parents had come to the Finger Lakes region from New England in the early nineteenth century; the father was a modestly prosperous farmer who had briefly served in the New York legislature.
Gillett developed an interest in chemistry while a student at Cornell University. After graduating with the B. A. degree in 1906, he spent the summer in the laboratory of the inventor Thomas A. Edison, who commended his analytical skill, and then returned to Cornell as a graduate student and instructor in physical chemistry and electro-chemistry. In subsequent summers and vacations he worked for the industrial research firm of Arthur D. Little. Gillett received the Ph. D. in chemistry in 1910.
From 1910 to 1912 Gillett was manager of the research department of the Aluminum Castings Company, Detroit, Michigan. In 1912 he moved to the U. S. Bureau of Mines as chief alloy chemist in charge of the field station at Ithaca, New York, a post he occupied until 1924. It was during this period that Gillett's main interest turned from chemistry to metallurgy. One aspect of his work at the bureau led to the development of the rocking arc electric furnace for melting brass and other metals, a development for which he received, in 1915, the first of his thirteen patents. Gillett moved to the Bureau of Standards in Washington, D. C. , in 1924 as chief of the Division of Metallurgy, where his reputation continued to grow. He was one of the founders in 1929 of the magazine Metals and Alloys and served as its editorial director until 1943. In 1929 Gillett was chosen as the first director of the new Battelle Memorial Institute in Columbus, Ohio, established by a grant from the will of Gordon Battelle "for the encouragement of creative research and the making of discoveries and inventions. " It was Gillett who determined that the Battelle Institute should concentrate on metallurgical research and on "practical" applications rather than abstract theory. He began by surrounding himself with outstanding individuals from every branch of metallurgy and physical science, drawing on the long associations he had made at the Bureau of Mines and the Bureau of Standards. Over the next several years the institute under his guidance carried on research in such areas as blast furnace technology, ceramics, and the use of electron diffraction to determine the surface properties of metals, quickly establishing a reputation as a world leader in metallurgical research. During these years Gillett continued to write prolifically for Metals and Alloys and other technical journals. At the time of his death, his list of publications included six books and over two hundred articles covering nearly every phase of the practice of metallurgy. Gillett was first and foremost a scientist and he begrudged the time away from his research demanded by the promotional and administrative aspects of the director's post. In 1934 he persuaded the Battelle Institute trustees to let him step down in favor of Clyde E. Williams, a chemist whom he had recruited from industry in 1930. Gillett remained at the institute as chief technical advisor under Williams. He continued his work with alloy steels, foundry problems, and heat treatment, and also studied metal fatigue, an important factor in aircraft structures. His pioneering study of the "creep" of metals, their gradual deformation and failure under stress at high temperatures, played a role in future space technology. In his research Gillett was able to draw upon, and sometimes to obtain fresh insights from a vast store of erudition which extended well beyond the field of metallurgy. He retired from the Battelle Institute in 1949 but remained a consultant until his death. Gillett died of a cerebral hemorrhage near Nicholasville, Kentucky, while returning from a hunting trip in the South. His remains were cremated and buried in the family plot at Penn Yan.
A thin, wiry man in a baggy sweater and with an ever-present pipe, "Gil, " as his associates affectionately knew him, was well qualified to organize and initiate a program of active and significant research. He had a quick perception and an awesome reading ability capable of detecting the smallest detail or error in a manuscript at a glance, an ability which extended to a half-dozen foreign languages, which he had taught himself.
Gillett married Carrie Louise Pratt, the daughter of a local manufacturer, at Penn Yan, New York, on April 18, 1911. They had three children.
