|“|| Dean: No, the right thing would have been to send your ass back home to your mom.|
Jo: [smiling] Like to have seen you try... He was right about one thing.
Dean: [smirking] What, your massive crush on me?
Jo: [laughs] Shut up!
— Dean and Jo
in No Exit
Dean Winchester and Jo Harvelle shared a friendship. Their relationship was damaged in "No Exit" and "Born Under a Bad Sign", although they moved on enough years later to renew their friendship when they met again in Season 5.
Dean and Jo's fathers, John Winchester and Bill Harvelle respectively, were fellow hunters. John sometimes visited Harvelle's Roadhouse, where the Harvelles lived and worked, and grew quite close to the Harvelle family; Jo's mother, Ellen, later described him as being "like family" at one point.
John and Bill went on a hunt together that resulted in the latter's death and the former's estrangement from the Roadhouse crew. John avoided the Roadhouse out of guilt and never told his sons Dean or Sam about it, the Harvelles' existence, or Bill's death. Due to this Jo gets mad and yells at Dean and Sam and quotes "like father like son" she than leaves and doesn't return until season 5.
- [Jo presses the barrel of a rifle against Dean's back.]
- Dean: Oh, God, please let that be a rifle.
- [Jo cocks the rifle.]
- Jo: No, I'm just real happy to see you.
Dean and Jo first met when Sam and Dean broke into the Roadhouse in "Everybody Loves a Clown" after tracing a voicemail Ellen left on their now deceased father's phone. When Sam left the room, Jo snuck up on Dean from behind and managed to subdue him. Once the Winchesters and Harvelles realized who the other party was, Dean automatically started to flirt with Jo, but he found himself too weighed down by the events of the previous episode to go through with it. Surprised, she remarked that he was different from other "scumbag" hunters. They agreed that any potential relationship between them then would be "wrong place, wrong time." However, Jo harbored a crush on him that she kept to herself.
When Dean and Sam next visit the Roadhouse, Dean chatted with Jo. She wanted to help him and Sam with their case, but he refused by claiming he was afraid of what Ellen might do to him, which amused Jo. He teased her back when she put on "Can't Fight This Feeling" by REO Speedwagon, which he later sang to himself when he and Sam drove away in the Impala.
Dean was impressed with the research Jo did for her case in "No Exit" to the point that he thought that computer genius Ash must have done it instead. When Jo went to work her case even after Ellen forbade it, she encountered the Winchesters already there to try to solve it. An irritated Dean played along with her claim that he was her boyfriend in order to fool the building manager, but once they were alone, he didn't want to let her join in on the hunt because she was an amateur. Jo managed to convince him to let her stay when her mother called to look for her.
Dean tried to watch over Jo while they hunted together. He also tried to persuade her out of trying to hunt before she ruined her life. Later, they shared what they remembered of their fathers and Jo explained to Dean why she wanted to hunt when he tried to give her a replacement for Bill's knife; after that, he became more sympathetic to her desire to be a hunter. He felt guilty when she was abducted by the ghost they were hunting, but eventually saved her and they trapped the ghost. When Ellen showed up angry at all of them, he tried to defend Jo by saying that she did well and Bill would've been proud of her.
However, Ellen then told Jo that John had accidentally gotten Bill killed. Jo was shocked and angry to hear this; when Dean tried to intercept her to learn why she was upset, she blew up at him before quietly ordering him to leave the Roadhouse.
Sam temporarily became possessed by the demon Meg, who commented that Jo still "carried a torch" for Dean despite her anger at him, and claimed that he only saw her as a little sister or a schoolgirl, which visibly upset Jo.
Dean eventually arrived, but refused to kill his brother in order to save Jo. He paused long enough to untie Jo before he chased after the fleeing demon. Jo later went looking for Dean to make sure he and Sam were alright, tracking his ringtone and finding him shot by Meg and almost drowned on a boat launch. She removed the bullet from his shoulder, bandaged the wound, and gave him medicine to help deal with the pain.
Remembering how Meg's words about Dean's lack of interest in her and the details of Bill's death, Jo asked Dean if demons sometimes told the truth as well as lies but wouldn't tell him what Meg had said. She wanted to help him exorcise Meg from Sam, but gave up when Dean threatened to tie her up himself to ensure she wouldn't get killed on his watch. She came to believe that he did not care about her like she did him, muttering, "No, you won't," when he left after saying he'd call her.
- Dean: Hmm. So, dangerous mission tomorrow. Guess it's time to eat, drink, and you know make merry.
- Jo: Are you giving me the "last night on Earth" speech?
- Dean: What?
- Jo: What?
- Dean: No... But if I was, would that work?
- [Jo leans in to kiss Dean, then suddenly pulls back]
- Jo: No. Sweetheart, if this is our last night on Earth, then I'm going to spend it with a little thing I call self-respect. [laughs and leaves]
- Dean: [muttering] If you're into that sort of thing.
Dean and Jo briefly encountered each other again in "Good God, Y'all"; after Ellen and Dean convinced Jo and Rufus Turner that War was making them hallucinate demons, they greeted each other and went about finishing the job.
In "Abandon All Hope...", Jo helped Dean and Sam break into Crowley's mansion to reclaim the Colt by luring out the demonic guards and subduing them. Afterwards, they gathered at Bobby's house for one last night together before trying to kill Lucifer. Dean took this opportunity to try to make a move on Jo, but despite her attraction to him, she turned him down due to the dire circumstances, embarrassing him. In the group photograph Bobby took of everyone, they put their arms around each other.
Later in the episode, when the hunters ran from hellhounds, Jo turned back against Dean's warning her to stay back, to fend off the hellhound attacking him, in the process getting torn open herself by another hellhound. Dean scooped her up and carried her into a nearby general store. He knew she was dying, but went into denial and tried to make a plan to save her, at which point she pointed out that the only solution was to build a bomb to kill the hellhounds while Dean and the other hunters escape and she stay behind to sacrifice herself. As much as it pained Dean, he saw the logic in this plan and did as she said.
Once the bomb was built, Dean gave Jo the trigger and told her he'd see her again in the afterlife, "Probably sooner than later," to which she replied, "Make it later." He kissed her on the forehead, then on the mouth, and lingered next to her before abruptly tearing himself away. As he left with Sam, he watched the store blow up in horror and sadness. After their attempt to kill Lucifer failed, they returned to Bobby's house and burned the group photo, with Dean focusing on Jo's face as it burnt up.
- Dean: It's okay.
- Jo: No, it's not. You deserve better.
- Dean: No, you did. You deserved better, Jo.
Jo's ghost was called as a witness to Dean's guilt when Osiris put him on trial. Osiris implied that she had had feelings for him, but she insisted that she just admired him and they just used to work together, saying that Dean was "kind of a jerk" as a person. Dean felt guilty about letting her do first case and how it had eventually led to her death. She tried to tell Dean she didn't blame him, but was dispelled by Osiris mid-sentence.
After Dean was declared guilty, Osiris sent Jo to kill him against her will. After teasing her about her massive crush on him, they tried to comfort each other and she told him that he carried too much guilt for circumstances outside his control. As she prepared to kill Dean, Osiris' hold on her broke because Sam had incapacitated him; she cupped Dean's cheek and smiled at him before vanishing. He closed his eyes in response to her touch and reopened them when he felt her disappear, then called out to her when he found her gone.
- The Supernatural writers developed Jo as a love interest for Dean, but ironically the two ended up never becoming a couple.
- Some members of the fanbase perceived Dean and Jo acting more like brother and sister, which got two nods in canon: in "Born Under a Bad Sign", Meg claimed that Dean saw Jo as a little sister, and in the alternate lives the angel Zachariah created for Dean and Sam, a memory-altered Dean believed that she actually was his little sister.
- Although the Dean/Jo pairing was largely unpopular among the fanbase in Season 2, it became more accepted in Season 5 in conjunction with Jo's spike in popularity.
- Dean was the third hunter whom Jo had feelings for, although their relationship was the only one shown on-screen; the other two (Rick and Gordon Walker) were only revealed in her online blog.
- "Defending Your Life" revealed that Jo is one of Dean's greatest regrets.