From 1596, when he was added to Henry's finance commission, Rosny introduced some order into France's economic affairs.
Acting as sole Superintendent of Finances  at the end of 1601, he authorized the free exportation of grain and wine, reduced legal interest, established a special court to try cases of peculation, forbade provincial governors to raise money on their own authority, and otherwise removed many abuses of tax-collecting.
Rosny abolished several offices, and by his honest, rigorous conduct of the country's finances, he was able to save between 1600 and 1610 an average of a million livres a year.

His achievements were by no means solely financial.
In 1599, he was appointed grand commissioner of highways and public works, superintendent of fortifications and grand master of artillery; in 1602, governor of Nantes and of Jargeau, captain-general of the Queen's gens d'armes and governor of the Bastille; in 1604, he was governor of Poitou; and in 1606, made first duke of Sully and a pair de France, ranking next to princes of the blood.
He declined the office of constable of France because he would not become a Roman Catholic.

Sully encouraged agriculture, urged the free circulation of produce, promoted stock-raising, forbade the destruction of the forests, drained swamps, built roads and bridges, planned a vast system of canals and actually began the Canal de Briare.
He strengthened the French military establishment; under his direction, the construction of a great line of defences on the frontiers began.
Abroad, Sully opposed the king's colonial policy as inconsistent with French interests, in opposition to men like Champlain who urged greater colonial efforts in Canada and elsewhere.
Neither did Sully show much favor toward industrial pursuits but, on the urgent solicitation of the king, he established a few silk factories.
He fought together with Henry IV in Savoy (1600–1601) and negotiated the treaty of peace in 1602; in 1603, he represented Henry at the court of James I of England; and throughout the reign, he helped the king to put down insurrections of the nobles, whether Roman Catholic or Protestant.
It was Sully, too, who arranged the marriage between Henry IV and Marie de' Medici.
From 1596, when he was added to Henry's finance commission, Rosny introduced some order into France's economic affairs. Acting as sole Superintendent of Finances  at the end of 1601, he authorized the free exportation of grain and wine, reduced legal interest, established a special court to try cases of peculation, forbade provincial governors to raise money on their own authority, and otherwise removed many abuses of tax-collecting. Rosny abolished several offices, and by his honest, rigorous conduct of the country's finances, he was able to save between 1600 and 1610 an average of a million livres a year.
His achievements were by no means solely financial. In 1599, he was appointed grand commissioner of highways and public works, superintendent of fortifications and grand master of artillery; in 1602, governor of Nantes and of Jargeau, captain-general of the Queen's gens d'armes and governor of the Bastille; in 1604, he was governor of Poitou; and in 1606, made first duke of Sully and a pair de France, ranking next to princes of the blood. He declined the office of constable of France because he would not become a Roman Catholic.
Sully encouraged agriculture, urged the free circulation of produce, promoted stock-raising, forbade the destruction of the forests, drained swamps, built roads and bridges, planned a vast system of canals and actually began the Canal de Briare. He strengthened the French military establishment; under his direction, the construction of a great line of defences on the frontiers began. Abroad, Sully opposed the king's colonial policy as inconsistent with French interests, in opposition to men like Champlain who urged greater colonial efforts in Canada and elsewhere. Neither did Sully show much favor toward industrial pursuits but, on the urgent solicitation of the king, he established a few silk factories. He fought together with Henry IV in Savoy (1600–1601) and negotiated the treaty of peace in 1602; in 1603, he represented Henry at the court of James I of England; and throughout the reign, he helped the king to put down insurrections of the nobles, whether Roman Catholic or Protestant. It was Sully, too, who arranged the marriage between Henry IV and Marie de' Medici.
Maximilien de Béthune, Duke of Sully