Otonas Jeronimas Piesliakas was born in Juodeliai village, Širvintai rural district, Ukmergė county. He finished primary school in 1940, later went to a progymnasium in Širvintos, and to Vilnius 1st boys’ gymnasium which he finished in 1948. In the same year, he became a student at the History-Philology Faculty of Vilnius University. His studies at the university were terminated by Soviet repression: in spring 1949, Otonas Jeronimas and thousands of other residents of Lithuania were deported to Irkutsk region in Siberia. In 1951, he wrote to the minister of education of Soviet Lithuania asking for help in regaining his school-leaving certificate. He intended studying in another institution of higher learning. Otonas Jeronimas Piesliakas returned from exile in 1957.