 He was born about 1180 the eldest son of Duke Berthold of Merania and his wife Agnes of Rochlitz.On the death of his father in 1204, he succeeded him as Duke of Merania, while the margravial titles in Istria and Carniola were inherited by his younger brother Henry II.On 21 June 1208, Otto married Beatrice II, Countess of Burgundy of House Hohenstaufen, daughter of late Count Otto I of Burgundy.