Among his siblings were his eldest brother Bruno, heir to their father's estates, and Liutgard, who in 876 became Queen of East Francia as consort of the Carolingian king Louis the Younger.

The charter described the region of South Thuringia, known as ‘pago Suththuringa,’ as ‘in comitatu Ottonis,’ which means 'in Otto's country.'

He succeeded his brother Bruno as duke of Saxony after the latter's death in the Battle of Lüneburg Heath (Ebsdorf) on 2 February 880, while fighting against the Viking invaders.

He remained a regional East Frankish prince and his lieges, Louis the Younger and Emperor Arnulf, with both of whom he was on good terms, rarely interfered in Saxon autonomy.

According to Widukind of Corvey, the "Saxon and Franconian people" offered Otto the kingship of East Francia after the death of the last Carolingian monarch, Louis the Child, in 911.