He served under four kings during his career, participating in the Siege of Calais (1558) and leading the royal army to victory in the third civil war at the battles of Jarnac and Moncontour.

[8] When the Peace of Cateau-Cambrésis brought an end to the Italian Wars in 1559, Tavannes was among those angrily denouncing it as a betrayal of the conquests he and other leading nobles had accomplished in the prior years.

Tavannes and Montmorency rushed onto the field to offer their assistance and removed Henri's mask to expose his bloody face with splinters embedded deep into it.

[11] In his role as lieutenant-governor of Burgundy, he prosecuted the Protestant population harshly, an action for which he was cautioned by Catherine de' Medici in 1561, who urged him to have patience.

[17] To support his military efforts in recapturing Chalons after it was seized by the baron des Adresse several thousand mercenaries would be hired from Switzerland and Germany.

[26] With the peace collapsing and the Protestant nobles moving into opposition, Tavannes allowed his correspondence on the matter to be intercepted by their agents, alerting them to the fact they were due to be arrested.

Whilst he opposed them politically he felt the planned arrest was a dishonourable method, the warning provided allowed them to flee south to La Rochelle and take up arms.

[27] During the third civil war he led the crown to victory at the battles of Jarnac and Moncontour commanding armies under the nominal leadership of Anjou.

[28][29] In the wake of the latter victory Tavannes and Cossé counselled the king to make peace while he had the advantage, but the government instead set about a siege of Saint-Jean-d'Angély.

[31] As one of Catherine's chief confidants and a member of the Conseil Privé he was intimately involved in the meetings that took place after the attempted assassination of Admiral Coligny in which the decision to liquidate the senior Protestant leadership was taken.