[2] His mother was a rich heiress, who had brought her husband the seigneuries of Avaux, Irval, Breuil, Besancourt, Bellefontaine, and Vandeuil.

[11] Strictly speaking, Claude de Mesmes therefore became comte d'Avaux only late in his life, in 1648, whereas his father never became count as he died in 1642, well before the registration date.

Fourth quarter: Or, chief gules, base azure waved, charge mullet sable (for Lassus in Guyenne).

In 1629 an Imperial army beleaguered and took Mantua, but the troops were soon recalled to Germany to fight in the Thirty Years' War (1618–1648).

Claude de Mesmes did not hesitate to spend money to enhance the prestige of France and his king: in October 1628 he celebrated the capture of La Rochelle by feasts and firework in Venice.

Richelieu feared that the Polish menace on their left flank would distract the Swedes from fighting the emperor in Germany.

This truce was to expire in July 1635[20] and the new Polish king, Władysław IV Vasa, seemed poised to resume the war.

[21] To ensure a timely renewal of the truce, Richelieu sent Claude de Mesmes to Poland as a mediator.

On the way Claude de Mesmes stopped in Copenhagen in 1634 to represent France at the wedding of crown prince Christian with Magdalene Sibylle of Saxony.

While in Copenhagen they received the news of the Swedish defeat at Nördlingen on 27 August (old style), which further weakened Sweden's position.

The negotiations had started on 24 January in the church of the small town of Holland (now Pasłęk) in Ducal Prussia.

However, King Władysław asked Douglas and Bergmann to make another attempt in which the French delegation participated.

[30] France supported Sweden almost right from the beginning of the Swedish intervention in the Thirty Years' War, which started in earnest with Gustavus Adolphus's invasion of Pomerania in 1630.

In the Treaty of Bärwalde in 1631 France promised a subvention of 1,000,000 livres (400,000 Riksdaler) per year to the Swedish army.

Richelieu sent d'Avaux (as he was called now) to Hamburg in 1638 to negotiate a new alliance with Johan Adler Salvius, sent by Queen Christina.

The negotiations led to the Treaty of Hamburg, signed on 15 March 1638, an extension of the alliance between France and Sweden for three year.

In 1643 he was sent to Germany to take part in the lengthy negotiations that eventually led to the Peace of Westphalia, which ended the Thirty Years' War.

[33] D'Avaux, who was more conciliatory, repeatedly clashed with Abel Servien, who was more demanding and had been dubbed "l'ange exterminateur de la paix" (the peace-killing angel) by the negotiators.

[36] This mansion stayed in the family until 1688, when it was sold to Paul de Beauvilliers, the future 2nd duc of St Aignan for 153,000 livres.

Although the dispute with Servien damaged his reputation, d'Avaux ended his career as a member of the high Council of the Realm and superintendent of finances[39] (1649–1650).

[40][f] Jean-Antoine also inherited his elder brother Henri's charge as président à mortier of the Parlement of Paris.