Swiss political philosopher of the Enlightenment and purported father of the French Revolution, Jean-Jacques Rousseau nonetheless made only one explicit contribution to economics - namely, his Discourse on Political Economy (1755) - which became the entry on the subject in Diderot's Encyclopedie. The article contains no obvious economic theory and is merely a pre-taste of the political philosophy he was to lay out in his Social Contract (1762). His earlier polemical Discourse on Inequality (1754) - which argued that civilization had destroyed man's "natural goodness" and thus was the source on inequality - is (un)remarkably prescient of the Marxian doctrine of "alienation", but, compared to Marx's careful analysis or those of the later Frankfurt School, Rousseau's is barely passable as a piece of socio-economics.
However little direct impact, Rousseau's work had a substantial indirect impact on economics. In particular, he shared with his fellow Enlightenment philosophers the faith in the existence of a "natural state" of society - which one could thereby extend to social equilibrium and "natural value" concepts - which were very much ingrained in the thinking of the Physiocrats and Adam Smith. His appeal to this state via his "natural man", the "noble savage", is reminiscent of the analogies formed in modern economics (think of Robinson Crusoe and equilibrium).
However, Rousseau did not push that idea as an analogy to the existing world - as so many economists did and still do. Rather, a thorough pessimist about existing human society, Rousseau recognized that this "natural state" was perverted by "civilization" and that the appetites and motivations of civilized man had been consequently corrupted and constructed by his interaction with society - "Man is born free and is everywhere in chains" as he wrote in his famous opening to the Social Contract. The "natural state", Rousseau claimed, could only be achieved via wholesale social reform which, in its ultimate manifestation, envisioned not Hobbes's "equilibrium" of competing wants, but rather a collective state with extra-personal dedication to a "General Will". Only in such a state, Rousseau asserted, could the true "natural man" exist and be truly free. It is these last observations that make Rousseau the putative father of Socialism (utopian and otherwise) - and earned him much emnity from later anti-Socialists such as Hayek.
The details of Rousseau's life are well-known (if a bit embellished in his Confessions): a citizen of Geneva, orphaned at ten after an idyllic childhood, apprenticed to a cruel watchmaker, Rousseau finally ran away from Geneva at sixteen and wandered around Europe until he settled himself in France as the lover of a bored lady, M. de Warens and a copier of music (and tutor to the young Abbé de Mably). In 1741, he moved to Paris and quickly fell into the Philosophes circle - Diderot, Voltaire, d'Alembert, and Mably's brilliant younger brother, Etienne de Condillac. He also knew the Physiocrats themselves, although he was not enthused by them. It was during this time that he picked up a poor mistress, Therese de Levasseur (later on, Rousseau abandoned their five children to foundling homes).
His first fiery Discourse (1750) was written as a submission to a competition at the Academy of Dijon. Later on, after his second Discourse on Inequality (1755), he broke with the Philosophes over his theory of civilizaton-as-corruption and left Paris for Montmercy in 1757 (see his polemical attack on them in the letter to d'Alembert). In the seclusion of the French countryside, he published his famous romantic novel, Nouvelle Heloise, his tract on education, Emile, his Social Contract and his treatise on revealed religion, Creed of Savoyard Priest. All this got him arrested and his books were burned throughout France. He ran off to England in the nick of time - being hosted and supported by David Hume - from which wrote his polemical Letters from the Mountain. However, Rousseau's paranoid nature and bitterness annoyed even the good-natured Hume, and soon enough, he returned to France, where he wandered in poverty until his death in 1778.
Then there was that commotion near the Bastille a few years later...
Major Works of Jean-Jacques Rousseau
Resources on Jean-Jacques Rousseau