Complex sentence: He left this ministry on 24 July 1754 to hold that of Foreign Secretary, in which role he signed the first Treaty of Versailles (1756) with Bernis, who suceeded him as Foreign Secretary (28 June 1757).
Split into simpler sentences: He left this ministry on 24 July 1754 to hold that of Foreign Secretary, in which role he signed the first Treaty of Versailles (1756). The Treaty's other French signatory was Bernis, who suceeded Rouillé as Foreign Secretary (28 June 1757).