The series features a girl named Sonny Munroe from Wisconsin, who moves w!. The series follows Sonny, her family and new friends in Hollywood and at the studio as Sonny will do her best to make new friends with the cast of the show, who all seem to like Sonny except for Tawni, because she does not want to share the spotlight with her. The show also revolves around So Random!s feud with MacKenzie Falls, a popular teen drama show which stars Chad Dylan Cooper. The series is almost a child-friendly version of 30 Rock, replacing writing for a sketch comedy with being on a sketch comedy. Also, in the pilot the cast of So Random! performs a bee sketch with costumes very similar to the ones used on Saturday Night Live, the show 30 Rock is based on. Now, the series is in its second season with the Channy relationship on the road.
- Sonny Munroe(Demi Lovato) is the newest cast member and a main character of So Random!. She was discovered on the internet. She is nice, caring and often a little goofy, and can be naive at times. She is from Middleton, Wisconsin. Sonny is friends with Nico, Grady, and Zora. She sometimes gets along with Tawni, although at other times she does not. She had a love/hate relationship with Chad but in the later episodes she gets to know him more and develops a crush on him. They began dating in "Falling for the Falls" only to break up in "Sonny With a Choice".
- Tawni Hart (Tiffany Thornton) is a very spoiled and snobby cast member of So Random! and can possibly be Sonny's new best friend. She dislikes Sonny at first because she doesn't want to share her spotlight, but later accepts her. Tawni hates people to know that she thinks Sonny is cool. She is all about fashion and wants everyone to do what ever she says . Tawni is probably the only one who knows about Chad's feelings for Sonny. Tawni becomes less spoiled and snobby than Season 1 after Chad and Sonny start dating.
- Chad Dylan Cooper (Sterling Knight) The teen heartthrob of Tween Weekly and MacKenzie Falls, and also the archenemy of Sonny and So Random!. He is also known as Chad Dylan Goldfarb. Though most people accuse him for being a jerk, other people think of him as cute and popular. As recently seen, he has shown his softer side to Sonny, and even the rest of the So Random! cast by helping them all break up Marshall and Bitterman. He is often seen teasing and arguing with Sonny but in most scenes where they are together alone he shows his softer side to her and shows that he cares about her. He's also a movie star, and a lot of times makes everything about him. He looks down on So Random!, a comedy show, unlike his show, MacKenzie Falls, which is a drama. He often refers to So Random! as chuckle city. MacKenzie Falls has the cool crew in Hollywood. Most of the times he wears the MacKenzie Falls uniform , but in other scenes he's seen wearing casual clothes. He had a love/hate relationship with Sonny. While he has a major crush on her and can't bear to see her with someone else, he seems unable to tell her how he feels, as seen in "Sonny With a Chance of Dating." They began dating in "Falling for the Falls" only to break up in "Sonny With a Choice".
- Nico Harris (Brandon Mychal Smith) is a cast member of So Random! and is best friends with Grady. He is side-tracked by girls easily and is very smooth. He is usually seen with a hat on that matches his outfit. He is also shown to have a minor crush on Sonny in earlier episodes.
- Grady Mitchell (Doug Brochu) is a cast member of So Random! and best friends with Nico . He always plays the "thing that comes out of Nico" in the So Random! sketches.
- Zora Lancaster (Allisyn Ashley Arm) is the youngest cast member of So Random!. She has a very weird and quirky personality, and always seems to be up to a suspicious scheme or project. She is also the smartest member of the cast, with a genius IQ. She devolops her first crush in Zora Blossoms.
- Connie Munroe (Nancy McKeon) is Sonny's mother. She is a bit strange, but gives good advice and cares a lot for Sonny, always wanting the best for her and is very supportive.
- Marshall Pike (Michael Kostroff) is the executive producer of So Random! who tries to act cool, making him appear to be the opposite. He still lives with his mother
- Portlyn Maddison (Jillian Murray) is a cast member of MacKenzie Falls. She's not always very bright. She disappears for no reason. The last episode to show her was Tales From the Prop House.
- Joy Bitterman (Vicki Lewis) is the teacher for the cast of So Random!, whose last name reflects her personality. She claims she has not laughed since she left the navy which may explain why she is so tense and bitter. But in The Problem with Pauly she laughs.
- Josh (Brent Tarnol) is the postman for the cast of So Random!.
- Lucy (Eden Sher) is Sonny's best friend in Wisconsin.
- Sharona (Elisa Donovan) is a mean celebrity blogger for Tween Weekly.
- James Conroy (Kelly Blatz) is a suave MacKenzie Falls guest star and also Tawni's ex-boyfriend.
- Murphy (Steve Hytner) is the offbeat security guard who takes his job a little too comically seriously.
- Santiago Heraldo (Rich Ceraulo) is an interviewer for Tween Weekly TV. He is the first person to give Sonny Munroe his first interview.
- Dakota Condor (G. Hannelius) is a very bratty little girl. She is in love with Chad Dylan Cooper. She made up the Children Having A Dream foundation in the episode "Sonny and the Studio Brat."
- Mr. Condor (Daniel Roebuck) is Dakota's father. He is the head of Condor Studios, the company that produces So Random! and MacKenzie Falls.