Maesa, like her sister, was probably of Arab descent. The were born in Syria, daughters of the priest Bassanius. Maesa married Syrian nobleman and military leader, Gaius Julius Avitus Alexianus and had two daughters, Julia Soaemias Bassania and Julia Avita Mamaea. When her brother-in-law Septemius Severus became Emperor, Maesa took her daughters and moved to Rome with her sister. Her husband served as Prefect and Tribune before being promoted to the Senate.
It was after the deaths of her nephew Caracalla and her sister Julia Domna that her actions became noteworthy in the eyes of the biographers. A man named Macrinus took the throne for a year and forced the family to return to Syria, but allowed them to keep their money. This proved a bad move on his part. Maesa resolved to keep power within her family and continue the dynasty her sister and brother-in-law had started. Together with her elder daughter, Julia Soaemias, she plotted to overthrow Macrinus and put her grandson Bassanius (later known as Elagabalus) on the throne, helped by the rumor that he was Caracalla’s illegitmate son.* Elagabalus took the throne and his mother unofficially ruled alongside him. Julia Maesa was proclaimed Augusta grandmother of Augustus.
This situation would not last long. Elagabalus and his mother were unpopular and their actions made them moreso. Maesa attempted to restrain her grandson, but when this proved impossible, cut her losses, and supported Alexander Severus, the son of her younger daughter, Julia Avita Mamea, instead. It was not too long after he was proclaimed heir that Elagabalus and his mother were assassinated. Maesa escaped this fate and put Alexander Severus on the throne. She and her daughter ruled as co-regents for the young Emperor. She died not long after, living to see the glory of her daughter and grandson’s rule, but not its bloody end.
*By contrast with Macrinus, who had no notable familial connections.