John William Mallet, chemist and teacher, the eldest child of Robert and Cordelia Mallet, was born near Dublin, Ireland, on October 10, 1832. He studied chemistry at the Royal College of Surgeons in Ireland in 1848 and received his Ph.D. from the University of Göttingen in 1852 and his A.B. from Trinity College, Dublin, in 1853. He moved to the United States that year and taught as assistant professor of analytical chemistry at Amherst College for part of 1854. He was appointed chemist to the Geological Survey of Alabama in 1855.
Mallet enlisted as a private in the Confederate cavalry in 1861 but soon was made an officer. In 1862 he was given general supervision of Confederate ordnance laboratories, with headquarters at Macon, Georgia. After the Civil War he taught chemistry in the medical department of the University of Louisiana, 1865–67, and at the University of Virginia, 1867–83. He was professor of chemistry and physics and chairman of the faculty of the University of Texas during its first session, 1883–84; the chemical library of that university is named in his honor. In 1884–85 he taught at Jefferson Medical College in Philadelphia and then returned to the University of Virginia, where he taught until 1908. He was professor emeritus until his death.
On July 21, 1857, Mallet married Mary Elizabeth Ormond of Tuscaloosa, Alabama, who died in 1886. They had three children. In 1888 he married Mrs. Josephine Burthe of Louisiana. Although he resided more than fifty years in the United States, he retained his British citizenship. Mallet was a fellow of the Royal Society, 1877, and one of the founders of the American Chemical Society. His published works include over 100 papers. He died on November 7, 1912.