A humanoid alien, PK, arrives on Earth for a research project in Rajasthan but finds himself stranded after losing the locket that serves as a beacon for his spaceship. Unfamiliar with human customs, he struggles to adapt, resorting to stealing money from couples in "dancing cars." In his quest to communicate, PK attempts to grasp people's hands to absorb their memories, but his intentions are misunderstood, and he is often chased away, perceived as a pervert.
In a twist of fate, the vehicle of Bhairon Singh strikes PK, leaving him unconscious. Bhairon takes him to a doctor who mistakenly diagnoses PK with amnesia, believing it to be a consequence of the accident. Sensing an opportunity, Bhairon initially considers abandoning him but changes his mind upon feeling pity, welcoming PK into his troop. As time passes, a friendship blossoms between the two. Misinterpreting PK's hand-holding as a romantic advance, Bhairon leads him to a brothel, where PK holds a prostitute's hand for an extended six hours, thereby learning the Bhojpuri language.
As PK ventures into Delhi searching for his lost remote, his peculiar behavior leads the locals to assume he's inebriated, coining him the nickname "PK" — which phonetically translates to "tipsy" in Hindi. Faced with the vastness of the city, desperate for guidance, PK seeks out God, only to be bewildered by the complexities and contradictions of Indian religions and customs. He discovers that a self-proclaimed God-man, Tapasvi Maharaj, possesses his remote and is falsely advertising it as the lost part of Lord Shiva's damru, which he claims to have found in the Himalayas. Tapasvi refuses to return the item despite PK's pleas, leading PK to conclude that such religious leaders are dialing the "wrong number" to God, propagating misunderstandings and useless rituals.
Meanwhile, in Bruges, Jaggu has fallen in love with Sarfaraz, a Pakistani man. Her father, Jaggu’s father, disapproves of the relationship and turns to Tapasvi for guidance, who ominously predicts Sarfaraz will betray her. With resolve to defy her father's wishes, Jaggu proposes to Sarfaraz. However, her hopes come crashing down when, at the chapel, she receives a letter breaking off the engagement due to their cultural differences. Heartbroken, she returns to India to become a television reporter and becomes intrigued by PK's quest to find a missing God. Infuriated with covering superficial stories, she persuades her boss, Cherry Bajwa, to allow her to investigate PK's story, which he reluctantly agrees to.
Jaggu devises a plan to expose Tapasvi and help recover PK's remote. She takes PK to a public Durbar held by Tapasvi, where PK methodically reveals that the calls to God are indeed going to a "wrong number," highlighting the fallacies in Tapasvi's claims. The public is swayed by PK's arguments, and Jaggu records the proceedings for national television, where PK declares that the so-called Managers of God are failing to solve real problems and advocates for people to assist one another.
As Tapasvi becomes aggressive towards PK and Jaggu, they manage to rally public support. Jaggu encourages the audience to submit their own experiences with religious leaders, branding them as "wrong numbers." Tragically, PK receives a phone call from Bhairon, who promises to visit Delhi but dies in a bomb blast set by extremists reacting to PK's outspoken protests against their faith. With a shocking confrontation looming, Tapasvi appears live on air, claiming direct communication with God. However, PK, having absorbed Jaggu's memories earlier, reveals that Sarfaraz did not, in fact, write the breakup letter. Determined to reconnect, Jaggu contacts the Pakistan Embassy only to find out Sarfaraz still loves her and reaches out regularly.
In the film's conclusion, as PK prepares to return to his planet, he quietly harbors feelings for Jaggu but refrains from confessing, knowing her affections lie with Sarfaraz. Instead, he records tapes of her voice, filling his suitcases with batteries to relive those memories on his home planet. Although she is aware of his true emotions, Jaggu remains silent and later pens a book about her experiences with PK. A year later, PK embarks on a new research mission back to Earth, accompanied by several other aliens.
