He fought for Henri III during the sixth war of religion under the nominal command of the king's brother Alençon seeing combat at La Charité-sur-Loire and Issoire.

He would again serve as ambassador to the Pope in 1598, during Henri's attempt to annul his marriage, though without succeeding in acquiring Papal approval.

The Estates General of 1576 had not however granted Henri any funds for this army, and resultingly it disintegrated due to desertions as the year continued.

After Issoire the army was in no condition to continue fighting, and Henri established peace with the Treaty of Bergerac on 17 September 1577.

An investigation was launched into the royalists that had made the request of Henri, while a letter was dispatched to Piney informing him they would not be in need of his services.

[13] The ligueurs on the council seized the moment, and on 9 February they ratified their membership of the Sainte Union in an extraordinary session.

Henri moved to quiet fears of his rule, promising to respect and protect the Catholic church, and to receive teachings in Catholicism in future.

This promise was sufficient for a core group of Catholic notables, among them Dinteville, lieutenant-general of Champagne, Marshal Aumont and Biron, the governor of Picardie Longueville and Piney, who swore their allegiance to him.

[16] In a letter sent to the terzo grandusco di Toscagne explaining the reasoning for Cathlolics to support Henri, Piney was among the signatories.

Venezia agreed to recognise Henri IV as king of France at this time, the first Catholic power in Europe to do so, and they dispatched their ambassador to him.

After this meeting, the ligueur Conde de Olivares and allied Cardinals attempted to convince Sixtus to have Piney dismissed.

[19] At their second meeting Piney assured Sixtus that Henri was not a true heretic, and that he was ready to abandon his errors if they were made known to him.

Sixtus was approving of what he heard, an attitude no doubt in part fostered by the military success Henri was experiencing currently after his victory at Arques.