Joanna Beth "Jo" Harvelle is the daughter of William and Ellen Harvelle. Her father died when she was a little girl during a hunt with John Winchester. She feels that being a hunter like her father is the best way she can honor his memory. After an argument with her mother about hunting, she moved to Minnesota and got a job as a bartender. She still continues to hunt. Once had a friendship with the Winchester brothers but after discovering it was their father that got her father killed and she walked away from them. It was upon this that Dean Winchester decided Jo's blood would never be on his hands. He refuses to hunt with her.

When Sam is possessed by a demon, he reveals to Jo that John may have actually killed her father after he was injured. It is also revealed that she has romantic feelings for Dean.

It is later revealed that Jo and her mother have been hunting together "for some time". They assist the brothers in stopping War, a horseman of the apocalypse.

Jo aids the Winchesters in retrieving the Colt from the demon Crowley. She and her mother join the brothers in their mission to kill Lucifer. When the four of them are attacked by a pack of hell hounds, Jo is mortally wounded while saving Dean. Once they get to safety, she tells her mother and the Winchesters not to try and save her, but rather to let her blow up the hell hounds, thereby sacrificing herself to give them a chance to get out. After setting up the explosives, Dean and Jo share a brief kiss. While Ellen initially agrees to the plan, she then says that she won't let Jo die alone, so the two of them sacrifice themselves so that Sam and Dean can escape.