Jimmy "B-Rabbit" Smith is the main protagonist and a young underground rapper who frequently performed in rap battles, well known for beating the rapper Papa Doc and becoming the new champion.
Nothing is known of his father and it is only slightly clear about what he was doing before the events of 8 Mile. According to Future he's a "lyrical genius" and would likely have been writing and performing songs for a few years. He was in a relationship with Jeneane, which ended just before the events of the film.
At the beginning of 8 Mile, we see him preparing for a rap battle at the Shelter (an underground club). He is clearly nervous and vomits before the show. He takes the stage to face Lil' Tic (Proof), but much to his embarassment he chokes and leaves the venue in disgrace.
The rest of the film focuses on his life and deciding about how he wants to make it in the rap game. After losing his job at a pizza parlour and splitting up with Jeneane, he's forced to move back in with his mother who lives in a trailer park with his young sister Lily. There is immediate heated conflict with his mother's boyfriend Greg who was at one time only a couple of years above Rabbit at school. Jimmy at some point started working at a pressing plant in Detroit in order to earn some money, but it was not enough for him to sustain himself properly; he was also scolded constantly at work by his boss for being late and not taking responsibility for this.
When he isn't working, he's seen hanging out with his friends Future (the rap battle host), Sol, DJ Iz and Cheddar Bob who are in their own way social outcasts and dream about finding their way out of the ghetto and living a life of luxury. His other friend Wink sees that B-Rabbit is a talented lyricist and rapper and has connections with WJLB a radio station that has access to studios and promotes the work of other artists. Wink is also an associate of The Leaders Of Tha Free World, a gang that serves as the primary antagonists of Jimmy and the rest of the 313 crew.
Whilst working one day he sees a blonde girl by the name of Alex Laterno who's looking for her brother. Immediately there is a spark between them. They meet again later on at a parking lot gathering and both end up at the proceeding abandoned house party. She reveals that she is an aspiring model with the intention of getting hooked up and going to New York. She shows up at his work one day during lunch break and witnesses him freestyling with some other employees. She is impressed and suggests he 'takes her somewhere'; they end up having sex in a hidden part of the plant. They start a brief relationship which essentially ends when he catches Wink and Alex having sex in one of the studios where Wink works, after Wink organises a photoshoot for Alex. A fight breaks out and Jimmy leaves. That night as Jimmy goes to collect his sister Lily (who was at a neighbors because their mother was intoxicated after Greg had left her following her impending eviction) he's confronted by Wink who has completely aligned himself with Papa Doc's gang and they proceed to attack him.
Meanwhile, Future has signed Jimmy up for another battle at the Shelter, much to his dismay at first, but he then decides that this is the best way to gain confidence and the respect of everyone in the battling community. He takes on two members of Papa Doc's gang in a battle (Lyckety-Split and Lotto) of whom he easily defeats with clever comebacks that are progressively impressive each time. Papa Doc being the defending "champion" allows B-Rabbit to battle first. B-Rabbit first starts the battle mocking Tha Free World before acknowledging any flaws that Papa Doc might have as ammunition against him (He lives with his mother in a trailer, he's "white trash", Cheddar Bob shot himself, Wink slept with his girl). In a smart twist, he uses these as a springboard to reveal to the crowd secrets about Papa Doc, i.e. Papa Doc wasn't a real thug but instead lead a privileged background complete with private schooling and a stable family environment. Humiliated and unable to make a comeback, Papa Doc leaves with the rest of Tha Free World crew. Jimmy decides to return to work instead of celebrating his battle victory and reveals to his friends that he plans to "make it on his own". He then leaves and it is implied that he would become what Eminem is now.
- Jeneane (last name unknown): Jimmy had a relationship with Jeneane. She thought they were going to split up, so she told Jimmy that she was pregnant. Jimmy does break up with her, but he says that it's not her, it's him. He left his car with her because he thought she was pregnant. She later comes to his job and asks him why he hasn't called. While talking to her, it is revealed that B-Rabbit never actually broke up with her and that he just left without saying a word. B-Rabbit says to go home; he can't talk about this now whilst he's at work. As she leaves, she makes fun of him.
- Alex Latorno: She is the brief love interest of Jimmy during the film. They first have sex at Jimmy's workplace. The relationship disintegrates when Jimmy finds her having sex with Wink. This leads to him fighting with Wink and his subsequent beating by The Free World crew. She does seem sorry for what transpired, and wishes him luck before his final rap battle. At the end they exchange a reconcillatory look and gesture.
- Stephanie Smith: His relationship with his mother has been one of emotional turmoil. She's an alcoholic who dates bad men, has no job, scrounges on welfare and is about to be evicted from their trailer. She somewhat feels guilty about about the life she's given Jimmy and Lily but can never really seem to get motivated enough to be able to turn it around. Things are at their worst between the two when they argue over Greg Buehl, an idiot redneck and fellow former pupil of Jimmy's school who is involved in a relationship with Stephanie at the start of the film. She blames him for Greg's later abandonment of her and seems to act like their current situation isn't really her fault. By the end of the film it is revealed that she went to bingo and won $3200 which was more than enough for her to pay the overdue rent and avoid losing her home. She somewhat seems keen to change her life for the better and reconciles with Jimmy.
- Greg Buehl: Jimmy first encounters Greg having sexual intercourse with his mother upon returning to the home. They instantly start to feud after Greg taunts Jimmy about his job at the pressing plant. Greg treats him disrespectfully throughout the film. When Greg finds out about Stephanie's eviction he begins to get violent with her; Jimmy intervenes and fights Greg causing him to leave and he is never seen again in the film.
- Lily Smith: Jimmy's younger half-sister. He behaves very tenderly and caring towards her, and makes her more of a priority than his mother does.
- Future: Future is the Battle Host at the Shelter. He is good friends with Jimmy and acts like something of a mentor, encouraging Jimmy to display his talent through freestyle battles. They have a brief falling out when Future signs him up to the next battle without his consent, but ultimately Jimmy decides to battle which leads to his success.
- Wink: Wink is another friend who also wants to help Jimmy, but by getting him into promo with demos and studio time. Him and Future don't get on and Future suggests that Wink frequently exaggerates or flat out lies about his connections. Wink is also connected to Tha Free World, which leads to conflicting interests. Wink helps Alex with her modelling work, but then has sex with her in the studio. Jimmy discovers them and fights Wink, which leads to Wink getting Tha Free World crew to beat up Jimmy. Although they don't make up, Wink is seen to smile when Jimmy wins the final battle, suggesting he is happy for his former friend.
- Cheddar Bob: A member of Jimmy's crew, Bob is portrayed as having some degree of learning difficulties. Jimmy acts as protector for Bob and Bob seems to idolise him.
- Sol: another friend and member of Rabbit's crew.
- DJ IZ: another friend and member of Rabbit's crew. He is portrayed as quite intellectual and will talk at length about the inequalities present in Detroit. He also seems to be a feminist.
- Paul: A gay man working with Rabbit, Rabbit sticks up for him when another worker is acting homophobically towards him. In return, Paul covers Jimmy's shift so he can battle at the Shelter at the end of the film.