Prosecutors say 53-year-old Kirsten Smith is scheduled to be arraigned on a murder charge Monday in Brockton District Court.
Police responded to the couple's home on Friday afternoon where they found 52-year-old Scott Benoit suffering from a stab wound to the chest. He was pronounced dead at the scene.
State and local police interviewed Smith until late Friday, when she was charged.
The Plymouth district attorney's office says a knife was also found at the scene.
Smith was held over the weekend and it was unclear if she had hired a lawyer.
The death was the city's fourth homicide of the year.