John Terrence Slattery (January 6, 1878 – July 17, 1949) was a catcher and first baseman for the Boston Americans, Cleveland Naps, Chicago White Sox, St. Louis Cardinals, and the Washington Senators for parts of four seasons between 1901 and 1909. He was never used regularly, and some of his Major League stops were very short (he played only four games for the Naps). He went to college at Boston College and Fordham University. From 1920 to 1923, he was head baseball coach at Harvard.