The two main settings show the work and home life of Rob Petrie (Dick Van Dyke), the head writer of a comedy variety show filmed in Manhattan. Viewers are given an "inside look" at how a TV show (the fictitious The Alan Brady Show) was written and produced. Many scenes deal with Rob and his coworkers, writers Buddy Sorrell (Morey Amsterdam) and Sally Rogers (Rose Marie). Mel Cooley (Richard Deacon), a balding straight man and recipient of numerous insulting one-liners from Buddy, was the show's producer and the brother-in-law of the show's star, Alan Brady (Carl Reiner). As Rob, Buddy, and Sally write for a comedy show, the premise provides a built-in forum for them to be making jokes constantly. Other scenes focus on the home life of Rob, his wife Laura (Mary Tyler Moore), and son Richie (Larry Mathews), who live at 148 Bonnie Meadow Road in suburban New Rochelle, New York. Also often seen are their next-door neighbors and best friends, Jerry Helper (Jerry Paris), a dentist, and his wife Millie (Ann Morgan Guilbert).
Robert "Rob" Simpson Petrie (Dick Van Dyke), the head comedy writer for a fictional New York TV variety series called The Alan Brady Show. The role of Rob Petrie was almost given to Johnny Carson, but Sheldon Leonard, the show's executive producer, suggested Van Dyke.
Laura Meeker/Meehan Petrie (Mary Tyler Moore), Rob's wife. A stay-at-home mom and former dancer in the U.S.O. (where she met Rob). The role of Laura proved to be the most difficult to cast. About 60 actresses auditioned for the part before Moore was signed, and she almost didn't go to the audition. Her original maiden name was Meeker, acknowledging Moore's then-husband Richard Meeker. After Moore and Meeker divorced, Laura's maiden name was changed to Meehan.
Maurice "Buddy" Sorrell (Morey Amsterdam) – an energetic (and at times facetious) "human joke machine" (as was Amsterdam himself), one of the comedy writers. Amsterdam was recommended for the role by Rose Marie as soon as she had signed on to the series. Buddy is constantly making fun of Mel Cooley (the show's producer) for being bald and dull. His character is loosely based on Mel Brooks who also wrote for Your Show of Shows. He makes frequent jokes about his marriage to his wife "Pickles." In several episodes, it is mentioned that Buddy is Jewish. He was identified by his Yiddish name, Moishe Selig, when he had his belated bar mitzvah in "Buddy Sorrell – Man and Boy." Additionally, Buddy owns a large German Shepherd named Larry (possibly named by the writers after Larry Matthews) and plays the cello.
Sally Rogers (Rose Marie), another of the comedy writers (and the comedy trio's designated typist), who is always on the lookout for a husband. The character was loosely based on Selma Diamond and Lucille Kallen, both writers for Your Show of Shows. She never drinks and quotes frequently from her "Aunt Agnes in Cleveland" (although the quotes seldom make sense). She has an on-again/off-again relationship with her boyfriend Herman Glimscher, who seems to be too much of a mommy's boy to get married. She frequently scares men off with her sense of humor and strong personality.
Richard "Richie" Rosebud Petrie (Larry Mathews), Rob and Laura's son. (His middle name is an acronym for "Robert Oscar Sam Edward Benjamin Ulysses David," all members of Rob's and Laura's families.)
Melvin "Mel" Cooley (Richard Deacon), the balding producer of The Alan Brady Show (and Brady's brother-in-law), who is constantly at odds with Buddy, who often makes insulting comments about Mel's baldness, to which Mel ofttimes responds with a simple "Yechh!" In reality, the two men, Richard Deacon and Morey Amsterdam, were very good friends and would work together to come up with many of the insults that Buddy hurls at Mel.
Jerry (Jerry Paris), a dentist by profession, and his wife, Mildred "Millie" Krumbermacher Helper (Ann Morgan Guilbert), the Petries' next-door neighbors. Three children have been named from the Helper family, Ellen, Patty, and Freddie.
Alan Brady (Carl Reiner), the egocentric, toupee-wearing star of The Alan Brady Show. Originally an offscreen character, then shown only with his back to the camera or only in voice, Brady began to make full-face appearances in the fourth season.
Stacey Petrie (Jerry Van Dyke), Rob's brother, banjo player, and one-time sleepwalker, played by Dick Van Dyke's real-life brother.
Fiona "Pickles" Sorrell (Barbara Perry/Joan Shawlee), Buddy's slightly nutty wife. She would become an offscreen character after Season 2.
Herman Glimscher (Bill Idelson), Sally's occasional and "nerdy" boyfriend. In the 2004 Reunion Special, Sally and Herman had been married for years. (In an early episode Sally mentioned having dated a Woodrow Glimscher, presumably a relative, until Woodrow's overbearing mother arranged for her to date Herman instead.)
Sam and Clara Petrie (Will Wright/J. Pat O'Malley/Tom Tully and Isabel Randolph), Rob's parents.
Mr. and Mrs. Alan Meehan (Carl Benton Reid and
Geraldine Wall), Laura's parents.
Freddie Helper (Peter Oliphant), Millie and
Jerry Helper's son and Ritchie's closest friend.
Sol Pomeroy, Rob's army buddy in flashback episodes, was originally played by Marty Ingels. Allan Melvin took over the role beginning in 1962 when Ingels left to star in I'm Dickens, He's Fenster. During the first season, Melvin had played another old army buddy, Harrison B. Harding, in a non-flashback episode. And, in the series's final installment, he played a gun salesman in an Old West dream episode.
Delivery Boy was originally a nameless character played by Jamie Farr in four Season One episodes. Subsequently, he was given the name Willie and Herbie Faye played the role. (Faye also played other characters in later episodes.)