John Bach McMaster (June 29, 1852 – May 24, 1932) was an American historian.
McMaster was born in Brooklyn, New York. His father, a native of New York, was a banker and planter at New Orleans at the beginning of the Civil War. He graduated from the College of the City of New York in 1872, worked as a civil engineer in 1873-1877, was instructor in civil engineering at Princeton University in 1877-1883, and in 1883 became professor of American history in the University of Pennsylvania. McMaster was elected a member of the American Antiquarian Society in 1884.
McMaster is best known for his History of the People of the United States from the Revolution to the Civil War (1883 sqq.), a valuable supplement to the more purely political writings of James Schouler, Von Holst and Henry Adams. He began working on it in 1873, having collected material since 1870. His A School History of the United States (1897) was an extremely popular textbook for many years. Besides these books and numerous magazine articles, he published Benjamin Franklin as a Man of Letters in the "Men of Letters" series (Boston, 1887). His historical work differed from standard practice in that it departed from an exclusively political focus to delve into social history and the lives of ordinary people and also in its use of news papers as sources.