William Hoskins was born in 1862 to parents John and Mary Ann Hoskins, in Chicago. Hoskins would complete just two of three years of Chicago High School; despite having an interest in chemistry, he would gain no formal education in chemistry throughout his early years. Hoskins, however, received "private instruction" in the field, before joining (at age thirteen), the Illinois State Microscopical Society. Four years later, at 17, the society elected him secretary.
After leaving high school in 1880 at age 17, Hoskins prepared chemical analysis samples for Chicago-based consulting and analytical chemist Guy A. Mariner in the latter's commercial laboratory, starting in February. Beginning in 1880, Mariner was one of only three completely commercial chemists in Chicago. Five years after joining the laboratory, Hoskins became Mariner's partner; the firm was renamed Mariner and Hoskins. Shortly before becoming the partner, Hoskins married Mariner's daughter, Ada Mae,[a] in December 18, 1883. In 1890, Hoskins became sole proprietor of the laboratory. The couple subsequently had four children: Minna, Edward, William and Florence.
In 1897, Hoskins began working with William A. Spinks before becoming a partner in William A. Spinks & Co. In the early 1900s, Hoskins would also become the director of Hoskins Manufacturing Co., based in Detroit, creating electric heating appliances and pyrometers. He was made a fellow of the American Association for the Advancement of Science (AAAS), and was also a charter member of the Chicago section of the American Chemical Society (ACS), of which he was the chairman in 1897, later becoming the national ACS's vice-president,. Hoskins Manufacturing eventually become Hoskins Process Development Co., of which he was the president. Hoskins became a recognized scientific expert witness in lawsuits, took out 37 US patents, and in Hoskins's lab, Albert L. Marsh developed nichrome under supervision of Hoskins. Hoskins's own innovations include a superior billiard chalk, materials used to construct race tracks (including the Washington Park Race Tracks in Chicago), safety paper for bank checks, a method for destroying weeds, and a gasoline blowtorch.