He carried out major reforms in the Russian Army and founded several elite military formations during the reign of Empress Anna of Russia (r. 1730–1740).

[4] In 1721, he was invited by the Russian ambassador in Warsaw, Alexey Grigoryevich Dolgorukov, for engineering projects of the newly acquired northern territories.

For his engineering and military-engineering achievements he was promoted to the rank of the General-in-Chief, in 1726 by Catherine I, and awarded the Order of Saint Alexander Nevsky.

In 1727, Münnich was appointed the Governor of Saint Petersburg city while the Imperial court was temporarily transferred to Moscow by Peter II.

During his governorship, Münnich improved the local ports, reinforced the newly established Peter and Paul Fortress (1703), and was thinking of building a bridge towards Stockholm.

Münnich revised the table of ranks and evened the salary of the Russian officers with the invited foreign military specialists.

In 1734, by the reference of Ernst Johann von Biron he was sent to take the city of Danzig (Gdańsk) and after a prolonged siege and evasion of Stanisław Leszczyński was heavily reproached.

In 1736, as the commander of the Russian army, he headed the Turkish campaigns, besieging the important ports of Azak (modern Azov) and Özi.

Münnich refused to resume the campaign the very next year, but he returned to the lower Dnieper steppes in 1737, and on 2 July, took the fortress of Özi with the help of the Russian artillery.

The siege of Özi was also later mentioned in the humorous stories about Baron Munchausen, based on the adventures of the page to Duke Anthony Ulrich of Brunswick, Hieronymus von Münchhausen.

[5] Threatening to burn down the capital of that Principality, the city of Iași, he forced Moldavian boyars to accept the annexation of Moldavia on September 16 [O.S.

Due to military losses of the Habsburg monarchy and worsening of political relationships with Sweden, the Russian court accepted French mediation and signed the Treaty of Niš (October 3) by which Russia had to return almost all captured territories, including those gained by Münnich in Moldavia.

[6] Münnich's victories in the Moldavian campaign was later mentioned in one of the Lomonosov's odes, considered to be the first poem of that kind in Russian literature.

Voltaire wrote for his part: "It was Prince Eugene of the Muscovites; he had the virtues and vices of the great generals: skilful, enterprising, happy; but proud, superb, ambitious, and sometimes too despotic, and sacrificing the lives of his soldiers for his reputation.