In 1754 Wall was recalled from London to
Madrid becoming
Minister of Foreign Affairs, after the death of
José de Carvajal. A few months later he played a part in driving Carvajal's successor the
Marquess de La Ensenada from office, thereby also helping
Huéscar and the British Ambassador, Sir
Benjamin Keene. Wall served as
chief minister until 1763, when the
Duke of Grimaldi succeeded him. The despatches of the British Minister, Sir Benjamin Keene, and those of his successor,
George Hervey, 2nd Earl of Bristol, contain many references to Wall. Though a constant partisan of peace and good relations with
Britain, Wall was firm in asserting the rights of the
government he served. During the early stages of the
Seven Years' War (1756–63) he insisted on claiming compensation for the excesses of British
privateers in Spanish waters. He frequently complained to British officials about the difficulties which these adventurers' violence was causing. As an
expatriate, despite having previously represented the
French Crown, he was often taunted by various French factions. Wall himself was more concerned that
Britain's colonial acquisitions from France could mean that
Spain's South American Empire was threatened. The new King
Charles III (1759–88) retained Wall as prime minister. When Spain declared War in 1761, Wall as prime minister naturally carried out his King's decree, although he later confessed to Lord Bristol, the British ambassador, some regret with the benefit of hindsight that he could see the failure of his efforts in preserving the peace. The close relations between Charles III and the French
Bourbon Kings later made General Wall's position as prime minister very trying. Yet King Charles, who detested changing his ministers, refused all Wall's requests to retire, till Wall exhorted himself in 1763 by elaborately affecting an imaginary eye disease. Throughout his Spanish government service Wall built a network of relationships which survived his tenure for several decades perhaps even helping Spain during the following reign of King
Charles IV. Among the relationships he developed were those with the Duke of Grimaldi, the
Count of Aranda, the
Count of Campomanes,
Manuel de Roda,
Cayetano Pignatelli, 3rd Marquis of Rubí as well as with various ambassadors from around Europe such as the
Counts of Fuentes, and also with commissioners from the colonies, like
Ambrosio de Funes Villalpando, Count of Ricla. Among his committed Irish supporters were the engineer
William Bowles (1720–84) who studied the geology of Spain,
Pedro Fitz-James Stuart, the
de Lacy family,
Alejandro O'Reilly, Arnold
later Lord Mahoney,
Carlos McCarthy,
Francis Nangle,
Ambrosio O'Higgins and
Bernard Ward, 1st Viscount Bangor. Wall extended friendship and knowledge with others such as
Francisco Pérez Bayer,
Jose Clavijo y Fajardo,
Benito Bails,
Celestino Mutis,
Jose Agustín de Llano y de la Cuadra (Spanish Ambassador to
Vienna under Emperor
Joseph II and nephew of one of Spain's First Secretaries of State),
Sebastián de la Cuadra, 1st Marquis of Villarías, numerous members of
Juan de Iriarte's family,
Bernardino del Campo,
Ambassador José Nicolás de Azara (a follower of William Bowles' work) and Juan de Chindulza. He was elected a
Fellow of the Royal Society in 1753. ==Retirement==