[1] He was born at the Château de Rosny near Mantes-la-Jolie into a branch of the House of Béthune a noble family originating in Artois, and was brought up in the Reformed faith, a Huguenot.

The young Baron of Rosny was taken to Paris by his patron and was studying at the Collège de Bourgogne at the time of the St Bartholomew's Day Massacre, from which he escaped by discreetly carrying a Catholic book of hours under his arm.

In 1576 he accompanied the Duke of Anjou, younger brother of king Henri III, on an expedition into the Netherlands in order to regain the former Rosny estates, but being unsuccessful he attached himself for a time to the Prince of Orange.

Once Henry IV of France's succession to the throne was secured (c. 1594), the faithful and trusted Rosny received his reward in the shape of numerous estates and dignities.

The king was on his way to visit Sully, who lay ill in the Arsenal; his purpose was to make final preparations for imminent military intervention in the disputed succession to Jülich-Cleves-Berg after the death of Duke John William.

[6] [7] Although a member of the Queen's council of regency, his colleagues were not inclined to put up with his domineering leadership, and after a stormy debate he resigned as superintendent of finances on 26 January 1611, retiring into private life.

[3] By his first wife, Anne de Courtenay (1564-1589), daughter of François, Lord of Bontin, he had one son, Maximilien, Marquess of Rosny (1587–1634), who led a life of dissipation and debauchery.

By his second wife, Rachel de Cochefilet (1566–1659), the widow of François Hurault, Lord of Chateaupers, whom he married in 1592 and who turned Protestant to please him, he had nine children, of whom six died young.

He went on a progress with James VI to Inchmurrin and Hamilton Palace, after the king had written to the Laird of Wemyss for the loan of his best hackney horse and saddle.

Nevertheless, he was an excellent man of business, inexorable in punishing malversation and dishonesty on the part of others, and opposed to ruinous court expenditures that was the bane of almost all European monarchies in his day.

He was implicitly trusted by Henry IV and proved himself the most able assistant of the king in dispelling the chaos into which the religious and civil wars had plunged France.

After Henry IV, Sully was a major driving force behind the happy transformation in France between 1598 and 1610, in which agriculture and commerce benefitted, and peace and internal order were reestablished.

They are very valuable sources for the history of their time and as an autobiography, in spite of their containing many fictions, such as a mission undertaken by Sully to Queen Elizabeth I of England in 1601.