Protagonist Om Prakash Makhija (Shah Rukh Khan) is a smalltime actor in 1970s Bollywood. He and his friend Pappu (Shreyas Talpade) are trying to succeed as leading actors. He is in love with the film actress Shanti Priya (Deepika Padukone), whom he eventually befriends after saving her from a fire on set. Later, Om overhears her argument with film's producer Mukesh Mehra (Arjun Rampal). It turns out that they are secretly married and she is pregnant with his child, and she wants to make their relationship public. Mukesh appears to agree, but then later murders her in a fire. Om tries in vain to rescue her, but ends up badly burnt and run over by actor Rajesh Kapoor, who was carrying his heavily pregnant wife to the hospital. Kapoor carries them both to the hospital, but as his wife gives birth, Om dies from all his injuries.
The plot then moves 30 years and we meet Om Kapoor (also played by Shah Rukh Khan), the son of Rajesh Kapoor and the reincarnation of Om Prakash, now a popular A-list actor. A chance encounter with Mukesh (now a successful international movie producer) and the discovery of the remains of the studios where Shanti died awakens the memories of his former life.
Furious for the fact that neither his past life nor Shanti's deaths received justice, OK decides to make Mukesh confess his crimes. His plan is simple: revive the production of the movie Shanti was going to star in, had Mukesh not killed her, then having someone masquerading as her roaming the studio to spook Mukesh until he breaks and confess on tape. OK even has the very good luck of finding a dead-on Shanti lookalike in one of his fangirls; but even with that help, making Mukesh nervous enough to confess is easier said than done...
This movie has the following tropes:
- Actor Allusion: Almost all the actors featured in Deewangi Deewangi use signature dance moves from their most popular movies.
- Adam Westing: Anyone who is not a fictional character are playing thinly-veiled parodies of themselves and the Bollywood film industry.
- And Starring: Bindu gets the "And" credit at the end, while Deepika Padukone gets the "Introducing" credit.
- Big "NO!": Om Prakash's mom shouts a big "Nahin!" when she hears he wants to change his name.
- Bilingual Dialogue: O.K. and Mukesh freely codeswitch between English and Hindi in their conversations.
- Birth-Death Juxtaposition: When Om dies in the hospital, a mother gives birth in the next room. The baby turns out to be Om reincarnated.
- Break the Cutie: Poor Om Prakash. A young junior artist who falls in love with top actress Shantipriya, his dreams are shattered when he discovers that Shantipriya is actually married to Mukesh Mehra, and has been married to him in secret for two years. He then witnesses her getting locked into a burning film set by Mukesh, and attempts to rescue her only to receive a savage beatdown by Mukesh's henchmen. By the time Om manages to break into the burning film set, he's already severely injured, but doesn't stop trying to save Shanti. But just as he's about to save her, Om is knocked out of the building into the streets by an explosion, and is then accidentally hit by a car with Rajesh Kapoor and his wife. Despite being brought to the hospital, he ultimately succumbs to his injuries, remembering happier moments with his mother, Pappu, and Shanti as he dies.
- Cameo Cluster: The "Deewangi Deewangi" dance number, diegetically set at a Bollywood party, features dozens of India's hottest stars at the time dancing with Shah Rukh Khan.
- Creator Cameo: Farah Khan is the woman who fights with Om Prakash at the beginning of the movie. Lampshaded:Farah Khan: Hey, who do you think you are, the star of the movie?
Om Prakash: Well, who do you think you are, the director?
- Crowd Song: Obviously since it's Bollywood.
- Do Not Call Me "Paul": Mukesh insists on being called Mike, because that's what they call him in Hollywood.
- Fan Nickname: In-Universe example: Om Kapoor's fans call him OK.
- Gratuitous English: Characters frequently inject English lines and phrases in otherwise Hindi dialogue for emphasis, not that this is uncommon in India.
- The Item Number: Parodied and lampshaded. Om Kapoor and the director of his movie have a discussion where OK forces the director to change the scene he is supposed to act for a disco dance number of this nature. Sure enough, the film immediately cues said musical number. Albeit in this case, this number has a reason of existence beside mere fanservice, since serves as a setup to show Om Kapoor's pyrophobia for the first time.
- Meta Fiction: The film is about reincarnation and the making and remaking of a film called Om Shanti Om, which is about reincarnation. It's also something of a Bollywood parody.
- Multilingual Song: "Deewangi Deewangi" is sung in Hindi but features English refrains.
- No Celebrities Were Harmed:
- Rajesh and Lovely Kapoor are probably parodies of Rajesh Khanna and his wife Dimple Kapadia.
- Om Prakash and Pappu sneak in a movie theatre, pretending to be Manoj Kumar. The "real" Manoj later arrives, showing his ID with him covering his face.
- Oscar Bait: Parodied when Om has to play a blind deaf-mute with no legs or arms. Sure, critics will love it but his fans will be bored.
- The Prima Donna: O.K. starts out a self-centered, bratty actor who shows up to sets late and demands the directors overhaul their visions for what he wants. After he wins a Best Actor award and remembers his past life, he resolves to do better.
- Product Placement: Maybelline is given much focus during Sandy's brief Makeover Montage.
- Rasputinian Death: Om is beaten down mercilessly by security guards, repeatedly. He still manages to rise up, and bursts into a burning house to save Shanti. An explosion knocks him not only away from her, but out of the building entirely and into a nearby street. And he still manages to rise up to his feet again, only to finally be mortally wounded when Rajesh Kapoor's car hits him accidentally.
- Red Herring: The movie makes you think that Sandy is Shanti's reincarnation. Turns out, Shanti never reincarnated, as she becomes a vengeful ghost delivering Karmic Death.
- Red String of Fate: Literally. Bela ties a red string around her son's wrist for luck, and it leads to his Meet Cute.
- Reincarnation: Om is reincarnated and looks exactly like he did in his previous life, complete with his tattoo becoming some sort of birthmark.
- Reincarnation-Identifying Trait: Om Kapoor's wrist bears a birthmark that looks like Om Prakash's tattoo. Since his face isn't shown until afterwards, this is the first indication to the audience that he is Om reincarnated. Later, Pappu realizes that OK is Om after hearing his awards speech, which Om had spoken thirty years prior.
- Rescue Romance: Downplayed in that they are both killed before anything comes of it, but a friendship blooms between Om and Shanti after the former saves her from a fire.
- Rule of Three: Three plot-relevant fires. First, the one in which Om first rescues Shanti, the second where Om and Shanti are killed, and the third where Mukesh dies.
- Self-Deprecation: The actors in the movie are pretty much making fun of themselves. Averted with the many cameos in "Deewangi Deewangi", which celebrates Bollywood and some of its finest talent.
- Terrible Interviewees Montage: The aspiring actresses who try out for Om Shanti Om are all horrible.
- That Reminds Me of a Song: At the Filmfare Awards after-party, OK's father tells him that he has a surprise for him: a musical number performed by many famous (real life) Bollywood actors and actresses. It has no relevance at all to the plot, which resumes after the song ends.
- Title Drop: The film's title is said in the English refrains of the "Deewangi Deewangi" number:''All the hot girls put their hands up and say, 'Om Shanti Om'!
All the cool boys, come on make some noise, and say, 'Om Shanti Om'!
- Underwear of Power: All the superheroes of the Mohabbat Man movie.
- Wag the Director: In-universe. When Om doesn't like the scene he's supposed to play, he makes the director change it for a disco dance number.
- Whole-Plot Reference: OK's plot to get Mukesh to confess is similar to Hamlet's Play Within A Play.
- Why Did It Have to Be Snakes?: OK has an aversion to fire, thanks to his previous life's attempt to save Shanti from a burning set.