His surname was Doria, but since he belonged to the ruling house of Arborea he is often dynastically called Bas-Serra, or Doria-Bas.
[1] He was born at Castel Genovese (modern Castelsardo) between 1378 and 1379 to Eleanor and Brancaleone Doria, a Genoese nobleman.
In 1387, his brother died under Aragonese captivity and Marianus became sole judge at a time when the Judicate of Arborea was at war with the Crown of Aragon.
On 24 January 1388, Eleanor signed a pact with Aragon which brought peace and safeguarded Marianus' rule.
Marianus was 14 years old in 1392 when his mother promulgated the Carta de Logu and he was declared of age.