Protestantism in France has existed in its various forms starting with Calvinists and Lutherans since the Protestant Reformation. John Calvin was a Frenchman, as well as numerous other Protestant Reformers including William Farel, Pierre Viret and Theodore Beza, who was Calvin's successor in Geneva. Peter Waldo (Pierre Vaudes/de Vaux) was a merchant from Lyons, who founded a pre-Protestant group. Martin Bucer was born to German minority in Alsace, which historically belonged to the Holy Roman Empire, but now belongs to France.
Hans J. Hillerbrand in his Encyclopedia of Protestantism: 4-volume Set claims the Huguenots reached as much as 10% of the French population on the eve of the St. Bartholomew's Day massacre, declining to 7-8% by the end of the 16th century, and further after heavy persecution began once again with the Revocation of the Edict of Nantes by Louis XIV of France.
Protestants were granted a degree of religious freedom following the Edict of Nantes, but it ceased with the Edict of Fontainebleau. Protestant minority has been persecuted, and a majority of Huguenots fled the country, leaving isolated communities like the one in the Cevennes region, which survives to this day.