Not much is known about his life until his attempted rescue of Ivan VI of Russia, except the fact that he was of aristocratic Ukrainian origin.

His family's estates had been confiscated in 1709 by Peter the Great because his grandfather had sided with Ivan Mazepa against the tsar during the Swedish invasion of Russia.

Mirovich's original intentions for doing so were to bring about his own fame for rescuing the true tsar, so that he could enjoy a better life.

However, he also became religiously motivated, placing upon himself the Christian duty of removing one whom he considered to be a usurper in favor of the rightful tsar.

Their plan consisted of having Ushakov come in to the fortress by boat with a fake decree from the Empress ordering the liberation of Ivan VI.

However, when Mirovich reached Ivan's casemate, he found that he had already been slain by the guards in charge of executing the Empress' secret order.