Gay Austrian fashion reporter Brüno (pronounced as Bruno; he claims to be nineteen years old, despite being played by the 37-year-old Cohen), is fired from his television show after disrupting a catwalk show during Milan Fashion week. Accompanied by his assistant's assistant Lutz (Gustaf Hammarsten), who adores him, he travels to the United States to become a superstar. To Brüno's disappointment, his pygmy lover Diesel (Clifford Banagale), with whom he had various forms of anal sex (edited out in some international versions to lower film classification), does not come along. When Diesel leaves Brüno at the airport, it is shown that Diesel has another lover. Brüno sees this, and decides to forget Diesel and continue to find fame.
Brüno tries to start an acting career, but he does not even perform acceptably as an extra on NBC's Medium. He then produces a pilot for a celebrity interview show, which he presents to a focus group audience. The pilot shows him dancing erotically, criticizing the appearance of Jamie-Lynn Spears' fetus with reality TV star Brittny Gastineau, and attempting unsuccessfully to "interview" actor Harrison Ford. The close of the program features a close-up shot of a penis being swung around, and its urethral orifice screaming "Brüno!". The audience intensely dislikes the show, with one viewer stating that the program was "worse than cancer". Brüno then attempts to become famous in various other ways. In an attempt to create a sex tape, he arranges an interview with Ron Paul (unwittingly "played" by himself) whom Brüno mistakes for drag queen RuPaul, and while the two wait for a staged technical problem to be fixed, Brüno starts hitting on Paul, who leaves angrily and calls him "queer as blazes" to his staff.
Brüno consults a spiritualist (Gary Williams) to contact the deceased Rob Pilatus of Milli Vanilli for advice. He uses the opportunity also to perform homosexual mime sex acts on the invisible Pilatus.
He consults charity PR consultants Nicole and Suzanne DeFosset to select a world problem he can tackle to maximize his fame with a minimum of effort. He selects the Israeli-Palestinian conflict, and flies to Jerusalem, where he interviews former Mossad agent Yossi Alpher and Palestinian politician Ghassan Khatib. In the latter interview, Brüno conflates hummus and Hamas. He also interviews another Israeli and Palestinian professors, that interview ending with Brüno singing and having the two caress each other's hands. He leaves and as he is waling down a Jerusalem street dressed in a flamboyant Jewish outfit, is chased by offended orthodox Jews. He next arranges a meeting with Ayman Abu Aita, subtitled as "terrorist group leader, Al-Aqsa Martyrs' Brigades". For the meeting, he goes to a location described as a Palestinian refugee camp in Lebanon, where he hopes to be kidnapped. Cohen (as Brüno) first insults Abu Aita's hair and then suggests that "King Osama" looks like a dirty wizard or a homeless version of Santa Claus. Abu Aita's translator orders Brüno to leave immediately.