French diplomat and soldier Michel de Castelnau, sieur de la Mauvissière, had as a young man served under local commanders in Piedmont and in Picardy.

After the Peace of Cateau-Cambrésis in 1559, he had entered the king's service and been sent on diplomatic missions in 1560 to England, Germany, Savoy, and Rome.

After the death of King Francis II he had been charged with accompanying the widowed queen, Mary Stewart, back to Scotland.

Castelnau had returned to France in 1562 to fight against the Huguenots in Brittany and Normandy.

In 1572, however, King Charles IX had sent him to England, Germany, and Switzerland to appease the anger aroused by the massacre of French Protestants on St. Bartholomew's Day.

From 1575 he has been Henry III's ambassador to Elizabeth I of England.

During his years in England, he has written his Mémoires, with an eye to the moral instruction of his son.

Covering the years 1559–70, they provide a well-informed account of the beginnings of the Wars of Religion.

He returns to France in 1585, when the Holy League is about to dominate Paris.

Because he refuses to join the league, he is excluded from official appointments.

The Holy League's popular support throughout France forces Henry III to placate it.

After three months of continuous effort, in order to avert a public breach between the crown and the Guises, Catherine de Médicis is obliged, by the Treaty of Nemours (July 1585), to commit the King to making war against the Huguenots.