Walter Stanley Haines (September 27, 1850 – January 27, 1923) was an American professor of chemistry, materia medica, and toxicology.
He taught at Rush Medical College in Chicago for almost 50 years, and was acclaimed for his teaching.
With Frederick Peterson, he published a comprehensive guide to medicine and the law, A Textbook on Legal Medicine and Toxicology, which went through many editions.
An early forensic scientist, Haines testified in a number of sensational trials, including those relating to the Haymarket bombing of 1886, the disappearance of Adolph Luetgert's second wife Louisa in 1897, and the suspicious deaths in multimillionaire Thomas Hunton Swope's family in 1909.