Marcia was the daughter of Lucius Marcius Philippus and an unnamed first wife. She married Cato the Younger in 63 BCE, becoming stepmother to his two children. She was known at this time as “a woman of reputed excellence, about whom there was the most abundant talk.” Marrying her proved a wise move. She was the one who managed to repair the friendship between Cato and a fellow Stoic named Munatius when it was torn apart by jealousy. Marcia also bore Cato at least two, maybe three children, one of whom was probably a son. In 59 BCE her father remarried to Atia Balba Caesonia, making Marcia stepsister to both Octavia Minor and the future Augustus.
Seven years after her marriage to Cato, Marcia remarried to a man named Hortensius, one of Cato’s followers and friends. The story goes that since he had no male heir and wanted to be more closely related to Cato, he went to him and asked to marry his daughter, Porcia. When Cato refused on the grounds that the age difference was too great* and besides, he didn’t want to break up another man’s marriage. Hortensius changed tactics, and asked to marry Marcia instead. To this, Cato consented, provided her father agreed as well. So Marcia married Hortensius and apparently bore him a son.
All of this turned into a minor scandal in Rome because after Hortensius died, Marcia inherited nearly everything. And where did she take her wealth? Back to Cato’s household. Many powerful people seem to have felt that Cato used Marcia to get Hortensius’ wealth. Whether the two actually remarried is uncertain, but when Marcia returned and Cato had to leave Rome because of the civil war, he put Marcia in charge of his household and all the people in it.
*By the time of Marcia’s marriage to Hortensius, Hortensia was already widowed and probably older than her stepmother.
**Hortensius being in his 60s while Porcia was about 20.
Appian, The Civil Wars, Book II - Lacus Curtius
Plutarch, Life of Cato the Younger - Lacus Curtius
Plutarch, Life of Julius Caesar - Lacus Curtius
Means, Thomas and Sheila K. Dickinson. "Plutarch and the Family of Cato Minor." The Classical Journal 69.3 (1974): 210-215. [Found on Jstor]