 He was the oldest of two brothers, with Kazimieras Sleževičius, who would grow up to become a geophysicist, born in 1890.That same year, their father, Feliksas Sleževičius died.Despite the early death of his father, and with the support from his aunt and uncle, Mykolas Sleževičius left for studies in Jelgava (then known as Mitau), graduating from the Jelgava Gymnasium in 1901.