McLaughlin received his bachelor's and law degrees from the University of Michigan. By 1903 he was a respected historian and was selected to be the first director of the Department of Historical Research at the newly created Carnegie Institution in Washington, D.C., a post he held for two years. In 1914 he was named President of the American Historical Association. He became an advocate for historians giving guidance on world events and toured the United Kingdom to support its efforts in World War I. McLaughlin specialized in American constitutional history. His first major book, Confederation and Constitution, 1783-1789 (1907), was a volume in the American Nation series planned and edited by Albert Bushnell Hart of Harvard University. His other major works include The Courts, the Constitution, and Parties: Studiers in Constitutional History and Politics (1912) and The Foundations of American Constitutionalism (1932), based on the Anson G. Phelps Lectures delivered at New York University. His magnum opus, A Constitutional History of the United States won the 1936 Pulitzer Prize for History. Among the many students whom he mentored at the University of Chicago was the historian Henry Steele Commager.
Waldo Gifford Leland, "Recollections (1951)" and "The Reminiscences of Wald Gifford Leland" (1955 oral history) in Peter J. Wosh, ed., Waldo Gifford Leland and the Origins of the American Archival Profession (Chicago: Society of American Archivists, 2011).