Dewey was born Melville Louis Kossuth Dewey in New York State, United States. He attended Amherst College, where, while working as a student librarian, he developed the Dewey Decimal Classification. With his friend and fellow librarian Charles Cutter, he helped found the American Library Association (ALA); both men spoke at the First Annual ALA Conference held in Boston, Massachusetts in 1876.
He was a reformer of English spelling and is notably responsible for the "American" spelling of the word Catalog (as opposed to the British Catalogue). He changed his own name from Melville Louis Kossuth Dewey to simply Melvil Dui. He is also credited with the invention of the vertical office file.
In 1883, Dewey became the librarian for Columbia University in New York City, where in 1887 he founded the first library school. He co-founded, edited and was a frequent writer for the Library Journal.