Omelian Pleszkewycz was born in 1908 near Sokal in western Ukraine, which had been part of Austria-Hungary and then Poland. The Pleszkewycz family in western Ukraine are descended from an officer in Ivan Mazepa's army who escaped into what is now western Ukraine following the defeat of Ivan Mazepa at the Battle of Poltava in 1709. Omelian Pleszkewycz's father, Ivan Pleshkevich, and grandfather Peter Pleshkevich were Ukrainian Catholic priests. His grandfather's uncle, Simon Pleshkevich, was a close friend of Markiyan Shashkevych (initiator of the revival of the Ukrainian language in western Ukraine) and was the first priest to ever give a sermon in the Ukrainian language in St. George's Cathedral, the mother church of the Ukrainian Greek Catholic Church ( Eastern Rite Catholic). Omelian's grandmother, Antonina Vakhnianyna, was the sister of Anatole Vakhnianyn, founder of Prosvita. Omelian was also a nephew of Kazimierz Świtalski, Prime Minister of Poland (1929).