Mia is the spouse of Ethan Winters, the main character in Resident Evil 7: Biohazard. A researcher for a criminal organization called The Connections, Mia was tasked with escorting a bio-weapon called Eveline to another facility. But the tanker crashes in a Louisianan swamp during a hurricane, with Mia infected by Eveline as they end up with the Baker family.
As the result of her infection, Mia lashes out at Ethan when he came looking for her. From that point on, Mia works with a woman called Zoe (who is revealed to be a Baker) and Ethan tries to save them by receiving hints from Zoe when she telephones him, while Ethan is having to deal with constant attacks perpetrated by the other Bakers. After using one of the two serums Zoe created to kill Jack Baker, Ethan used the remaining vial on Mia as they are forced to leave Zoe behind.
The two end up at the remains of the tanker, Mia regaining her memories while resisting Eveline to give Ethan samples from Eveline to develop a toxin to kill her with. She is reunited with Ethan after being rescued by BSAA agents, later giving birth to Rosemary while not telling Ethan the truth that he was infected with the Mold as they moved to Eastern Europe.
In the events of Resident Evil Village, Mia is abducted by her former colleague Miranda, who assumed her identity to steal Rose as a vessel for her lost child Eva. Mia ends up being rescued by Chris Redfield and revealing Ethan's altered nature when told that Jack Baker killed him. After Ethan permanently died destroying the megamycete, Mia raised Rosemary while Chris would later train the girl in using her abilities.