Educated by Jesuits and Mikołaj Krzysztof "the Orphan" Radziwiłł, Pac joined the military at a young age and rose through its ranks to fight against Russian, Turkish, and Swedish armies.

[2] In 1663, during the Second Northern War (Deluge), when the territory of the Commonwealth was occupied by Russian and Swedish soldiers, Pac was appointed as the Field Hetman of Lithuania and voivode of Smolensk.

[3] Known as a "soldier of Christ" (miles Christi), Pac was a zealous and ambitious military leader; as the commander, he used to receive the Great Hetman Paulius Sapiega only while lying in bed, and constantly argued with king Sobieski and made fun of him in public.

After the death of Wiśniowiecki, he opposed the election of John III Sobieski, creating an opposition group consisting of the Oginski magnate family and Krzysztof Zygmunt Pac against the Radziwiłł and Sapiehas.

[5] Michał Kazimierz Pac funded the construction of St. Peter and St. Paul Church in Vilnius, considered to be one of the best examples of Baroque architecture in Europe.