He was introduced to court life by the duke of Guise shortly before Henri III departed as king of the Commonwealth.

Quickly detached from Guise's entourage, he joined his new patron as king in the east, before returning with him to France upon the death of Charles IX.

By the sixth civil war he had been elevated to the role of maître de camp of the light horse, in the hopes of frustrating Guise's control over the crown's cavalry.

In this capacity he fought in Auvergne in 1577, and wrangled with the Parlement of Bourdeaux which did not trust him, leaving him isolated and vulnerable to the rebel Navarre.

By 1578 Saint-Mégrin had been elevated to gentilhomme ordinaire de la chambre of Henri III, affording him considerable access to the king.

[7] He struggled vainly against the forces of the king of Navarre in Angoumois, his plight not assisted by the opposition of the Bourdeaux Parlement.

Saint-Mégrin found an ally in the seigneur de Lanssac, governor of Blaye, who afforded his troops entry despite the prohibition of the Parlement.

[1] This appointment was aimed at counterbalancing the authority the duke of Guise held over the light cavalry, in his capacity as colonel general.

Saint-Mégrin succeeded another royal favourite in the position, La Guiche, who was granted the role of Grand Maître of the artillery in compensation, a title usurped from the baron de Biron.

Further cause for Guise's displeasure came in the disrespect Saint-Mégrin showed to the man who had introduced him to court, and the presumptuousness of his social inferior to treat with him as an equal.

[16] Nevertheless, the Guise had departed court a month before the assassination in June, and would not return until March 1579, at which time they brought 700 horse with them, to restrain the king from exercising any vengeance.

[18] It is possible that Henri had promised Saint-Mégrin the position of lieutenant-general of the Angoumois and Saintonge prior to his death, however his assassination cut any plans to that effect.