She was married to Gessius Marcianus and gave him a son, later emperor Alexander Severus. Unlike her sister, Julia Mamaea was reported to be a virtuous woman, never involved in scandals. As a member of the Imperial Roman family, she watched closely the death of her cousin Caracalla and the ascent to power of her nephew Heliogabalus, the oldest grandson of Julia Maesa and her choice to the throne. But eventually Heliogabalus and his mother Julia Soaemias proved incompetent rulers and favour fell on Alexander, Julia's son. He became emperor in 222, following Heliogabalus murder by the Pretorian guard. Julia and her mother became regents in the name of Alexander, then 14 years old. After his adulthood, Alexander confirmed his esteem for his mother and named her consors imperii (imperial consort). It was in this condition that she accompanied her son in his campaigns: a custom started with Julia Domna (Septimius Severus's wife). Thus she travelled to the East, for the campaign against the Parthian empire, and to the Germania provinces. Julia Mamaea was with Alexander in Moguntiacum (modern Mainz), capital of Germania Superior, when he was assassinated by his troops. She suffered the same fate.
See also: Women in Rome – Severan dynasty family tree