The tale begins with a description of a region of Italy called Saluzzo. The Cleric describes a marquis of this region called Walter. Walter was so fixated on seeking instant pleasure that he forsook all other long term duties, including marrying. Eventually, his people beg him to take a wife so he can have children and secure his dynasty. Walter agrees, but on one condition: he can choose anyone he wants and his wife will be treated with the respect she deserves as his wife. The people agree and Walter sets a date for his wedding.
In a nearby village, a poor man, Janincula, lived, with his daughter Griselde. You've guessed it - Griselde was beautiful and also virtuous. Walter had caught sight of her during a hunting trip and decided Griselde would be his wife. He prepared beautiful clothes in Griselde's size and asks Janincula for her hand in marriage. He then asks Griselde for her permission, saying he will marry her if she agrees to do whatever he says without resenting him. Griselde agrees and they get married and Griselde has a girl as a firstborn, even though she would have preferred to have a boy.
Soon after this Walter decides to test his wife. The narrator says he can't understand why Walter would do this and says it is evil to do so. Walter says to his wife that she was not accepted by the rest of the nobility and therefore her daughter must be put to death. Griselde accepts this steadfastly, even though secretly Walter puts their daughter with a family member to be brought up and never mentions their daughter again.
Years passed, and Griselde had a boy. Walter does exactly the same thing with the boy, and the boy is taken away. Griselde accepts this. Walter then devises another "test" - he organises a counterfeit order from Rome ordering him to divorce Griselde, in spite of the fact that his people now hate him as they think he has killed his children. Meantime, he orders that his children be brought back to his city with great pomp and circumstance, but without revealing who they were. In fact, he let it be known that he would marry his daughter to continue this disguise.
Walter tells Griselde about the "divorce" and returns her dowry and sends her back to her father's house. Griselde accepts this without suffering, saying she will never repent loving Walter, and asking to go back in a simple smock. The people follow her as she returns, mourning her loss.
Walter's children arrive and Walter asks Griselde to plan his new wedding - to their daughter. Griselde does this patiently but at the wedding feast asks Walter to treat his new bride better than he has treated her. Walter then kisses her and reveals the deception, and they all live happily ever after.
The Cleric says the point of his tale is that we should all be faithful and steadfast against times of trial. He also says that women with the character of Griselde are very rare nowadays.