Last Tuesday, the former California governor admitted to fathering a child with a long-time member of his household staff.
The mother of Schwarzenegger's secret love child is believed to be his former housekeeper Mildred Patricia Baena, who retired from working at the Austrian star's home in January.
Shriver's only public comment so far has been to call for privacy at this "painful and heartbreaking time".
Just days after Schwarzenegger's spouse apparently hired prominent attorney Laura Wasser as her new representation, a source has now told Entertainment Tonight that Shriver has decided to divorce the Austrian actor.
It is thought that she could file legal paperwork to end her marriage as early as this week.
Neither Schwarzenegger nor Shriver have commented on the matter.
Yesterday, the couple's 21-year-old daughter Katherine asked the press to respect her family's privacy in the wake of her father's admission of infidelity.
> Maria Shriver 'refuses to hide' from scandal
> Jane Seymour: 'Schwarzenegger has more children'