In relation to politics, the term left wing originates from the French Revolution, when radical Montagnard deputies from the Third Estate generally sat to the left of the president's chair, a habit which began in the Estates General of 1789. The moderate Feuillants generally sat to the right.

It is still the tradition in the French Assemblée Nationale for the representatives to be seated left-to-right (relative to the Assemblée president) according to their political alignment. In some European countries classical liberals were labeled as 'left' before Marxist ideas came to define the left.

In the case of Denmark and Norway the historical liberal parties still carry the name Venstre (literally meaning 'Left') even though they are now considered to be right-wing. A similar phenomenon exists in France, where it is known as sinistrisme.

From mid-19th century, 'left' would increasingly refer to various forms of socialism and communism. Particularly influential event was the publication of the Communist Manifesto by Karl Marx and Frederick Engels in 1848. It asserted that a proletarian revolution would overthrow bourgeois society, and by abolishing private property create a classless and stateless society.

Socialist movements emerged across Europe and some countries outside of Europe. The International Workingmen's Association (commonly named the 'Second International') gathered labour parties with a combined membership of millions.

During the First World War, the Second International was divided on the question of supporting or opposing the war. The dissident tendency, which included the Russian Bolsheviks of Lenin, Rosa Luxemburg in Germany amongst others, considered themselves as further to the left that the other labour parties.

Out of this conflict the socialist movement divided into Social Democrats and Communists, the former category either seen as left or center-left. In the 1960s with the political upheavals of the Sino-Soviet split and the May 1968 revolt in France, thinkers of the 'New Left' viewed themselves as being more critical of Marxist and Marxist-Leninist discourse (labelled the 'Old Left').