Patrick Karl O'Brien FRHistS FBA (born 12 August 1932) is a British historian who serves as professor emeritus of global economic history at the London School of Economics and Political Science. He received a DPhil from Nuffield College (University of Oxford) in 1960 for a thesis entitled Government Revenue, 1793–1815: A Study of Fiscal and Financial Policy in the Wars Against France (supervised by Sir John Habakkuk and Max Hartwell).