A leading figure of the British school of economics of the 19th century, John Stuart Mill (1806-1873), son of economist James Mill, followed the path of Adam Smith and David Ricardo in his Principles of Political Economy which were a classic textbook. His essay "On liberty" is a famous libertarian piece.
On liberty, available from the Libertyfund Library of Economics and Liberty.
Principles of political economy, available from the Libertyfund Library of Economics and Liberty.