Born into a noble Briard family, Beauvais-Nangis began his military career at a young age, serving during the third French War of Religion at Jarnac and Moncontour, among other engagements.

Upon Anjou's return to France as King Henri III, Beauvais-Nangis was elevated as commander of the Picard regiments during the fifth War of Religion.

Henri felt obliged to disgrace him, and in March of that year, he was relieved of the post of Maître de camp.

In 1584, the king's brother Alençon died, and with the heir to the throne now the Protestant Navarre, a Catholic ligue formed in opposition.

Beauvais-Nangis was already disillusioned with the ligue which had failed to deliver him the office he desired and was fairly easily brought back into the royal orbit.

In 1587, he entered the royal council, and he participated in the royalist attempt to suppress the ligue in Paris, which resulted in humiliation for the king.

In the war with the ligue that followed the assassination, Beauvais-Nangis fought loyally for the king and was rewarded with the office of admiral in February 1589.

[5] His nephew Jacques de La Fin would be a favourite and agent of Henri III's brother Alençon.

[8] In his youth, Beauvais-Nangis completed his studies at the Collège de Lisieux [fr] in 1564 before entering the Paris Academy to learn how to fight.

D'Aumont occupied a relatively independent position in the court, propped up by the esteem for his long service and military experience.

On 11 March 1569, two days after participating in the Battle of Jarnac, Anjou named him a gentilhomme de la chambre, impressed by what he had seen on the field.

He served then as a guidon in an ordinance company for the Duke of Angoulême, an illegitimate son of Henri II, seeing service at the decisive royal victory of Moncontour the following year.

[11] Alongside serving the Duke of Anjou as gentilhomme de la chambre, he would also hold the role of chambellan for the prince.

[14] The siege would drag on, before Anjou's election as king of the Polish-Lithuanian Commonwealth allowed him to bring it to a close by negotiated settlement.

[16] Anjou was displeased that Beauvais-Nangis departed from him for a second time to crusade against the Devlet-i ʿAlīye-i ʿOsmānīye along with the Duke of Mayenne and Jean de Saulx, criticising their behaviour.

He bemoaned the betrayal of men who had demonstrated more loyalty to Marshal Bellegarde than him and drew up a list of those upon whom he felt he could rely for political support.

[20] In November of that year, the Maître de camp of the French guard, a very prestigious military post, was vacated by the murder of its incumbent Du Guast.

He would, however, refuse take the oath required for the role at the hands of François d'O, the premier gentilhomme de la chambre, greatly disliking this favourite of Henri.

The men looked to Beauvais-Nangis to secure their release, however he was unable to do so, and they remained in captivity until peace was made three months later.

Beauvais-Nangis was incensed by this as the honour of such a position theoretically belonged to the guards regiment, of which he was the Maître de camp.

When his father-in-law Barbezieux, the lieutenant-general of Champagne sought to resign his charge to Beauvais-Nangis, the young favourite refused the post, fearful that, if he were away from the king, his disgrace would become inevitable.

[35] The king's brother Alençon was increasingly set on his Dutch ambitions, and to that end raised troops during June 1581 for the purpose of entering Nederland.

[37] In June 1584, the king's brother Alençon died, and as Henri did not have any children, the succession defaulted to his distant cousin, the Protestant Navarre.

[38] It was to the end of joining this ligue that Beauvais-Nangis was approached by de Rosne and Sennecey, in their capacity as members of the Lorraine network.

[43] Beauvais-Nangis would be one of the nobles detached from loyalty to the ligue in 1586, alongside Entragues, d'O and the Duke of Nevers, who was secured for the crown by Catherine de' Medici.

The forces would meet bitter opposition from Parisian ligueurs who successfully drove them from the streets and threatened to capture the king in response.

To this end, he assembled a small council of himself, Alphonse d'Ornano, Rambouillet, and Maintenon, and it was agreed to assassinate the Duke of Guise by 3 votes to 1.

Historians have raised a degree of scepticism about this account of Beauvais-Nangis' role, seeing in it a desire to aggrandise his foresight and importance with the benefit of hindsight concerning what would actually follow the assassination.

The Estates General, which was finishing its deliberations, ruled that the office could not be kept in the Nogaret family through the Seigneur de La Valette who would thus have to resign the charge.

[37] In 1595, Beauvais-Nangis received the honour of being made a chevalier of the Ordre du Saint-Esprit, meaning that he was now in receipt of both orders of the king.