The French philosophers of the Enlightenment Era didn't play an active role in the events of the revolution, but their ideas inspired the revolutionary movement. The main philosophers were Voltaire, Rousseau, Diderot and Montesquieu.
Diderot was the editor of a ground-breaking Encyclopédie, which brought awareness to the inequality in France by describing some of the injustices of the ancien régime (the system of monarchy). Its promotion of individual rights influenced the revolutionaries.
Montesquieu proposed the idea of a system of checks and balances, whereby a monarch should not operate with absolute power, but limits (e.g. a constitution, parliamentary bodies). There should be a separation of powers, he believed, into 3 branches: legislative (they make the laws), executive (they enforce the law) and judicial (the court system). This inspired revolutionaries to demand this form of government in France, and to act in outrage against the absolute monarchy at the time.
Voltaire's main ideas revolved around individual liberties. He believed that people should have freedom of expression, religion, movement, the press, etc. He spoke out against the financial inequality and the government oppression in France. His ideas inspired revolutionaries to seek greater liberal rights and liberty.
Rousseau was the most radical of the philosophers. He believed in a rudimentary form of socialism. He believed that the ideal society would exist where there was no class distinction, no inequality, and everyone would work together towards ensuring the common good. He believed that the current monarchical system in France reduced people's liberties. He also believed that in a state of nature, a man untouched by civilization would act morally, this idea is sometimes confused with the idea of the "noble savage" a native who seemed to share the morality of the then current Europe. He believed that the French aristocracy was the embodiment of the corruption created by societal structure.
Source: Century of Change: Europe from 1789 to 1918 by E. Alyn Mitchner and R. Joanne Tuffs
There are two schools of thought on this matter regarding the French Revolution.
The first is that they had No Role. This holds true if it is seen as a popular or grass roots revolt by the man on the street seeking bread and hope for an improved life for his family. (Call this the Bastille Revolt). The peasant could not read or write and had little knowledge of or interest in philosophy or enlightenment theory. He also had no time to indulge in such frivolity. His life was a drudgery. He worked a twelve hour day and could still not feed his family.
The alternative is that it was the Guiding Light and focus (Call this the Tennis Court Oath Revolt). The people representing the Third Estate at the meeting of the Estates General were not illiterate peasants, but learned men and politically savvy. They were bright and articulate public leaders and they were familiar with the works of Locke, Voltaire and Rousseau. These were Doctors, Lawyers, Merchants and Bankers with as little knowledge of the plight and problems that faced the peasant as did the King. They were well aware of world affairs and they were in a position to act. They seized the revolt as their cause.