Advertising executive Bill Compton (Dennis Patrick), his wife Joan, and daughter Melissa (Susan Sarandon) are a wealthy family living in New York's Upper East Side. Melissa has been living with her drug dealer boyfriend. After Melissa overdoses and is sent to a hospital, Compton goes to her boyfriend's apartment to get her clothes. He confronts and kills the boyfriend in a fit of rage. At a nearby bar he hears factory worker Joe Curran (Peter Boyle) ranting about how he hates hippies, and blurts out that he just killed one. Joe reacts favorably, but Compton says it was a joke.
A few days later, Joe sees a news report about a drug dealer found slain a few blocks from the bar. He calls Compton and meets him. At first Compton is wary that Joe may be attempting blackmail, but Joe assures him that he admires Compton for killing the drug dealer. They become friends, and Compton and his wife have dinner at Joe's house with his wife. Melissa escapes from the hospital and returns to the family apartment, where she overhears her father discussing the murder. She storms out of the apartment house, saying to Compton, "What are you gonna do, kill me too?" Compton tries to restrain her, but she breaks away.
Joe and Compton search for her, and meet a group of hippies at a bar in downtown Manhattan. They join the hippies at an apartment, where the hippies share their drugs and girlfriends with the pair. They then abscond with drugs brought by Compton, which he had taken from the drug dealer, as well as Joe's and Compton's wallets. Joe beats one of the girls until she tells him that their boyfriends often spend time in an upstate commune. Joe and Compton drive to that commune, with Joe bringing rifles. In a confrontation at the commune, Joe and Compton kill all the hippies there, and Compton unwittingly kills his own daughter.
The film has garnered both critical acclaim and box office success. Produced on a tight budget of only $106,000, it grossed over $19.3 million in the United States, making it the 13th highest-grossing film of 1970. Joe received mostly positive reviews from critics, earning an 86% "Fresh" rating on the review aggregate website Rotten Tomatoes. Norman Wexler's screenplay received an Oscar nomination for Best Original Screenplay.
When Peter Boyle saw audience members cheering the violence in Joe, he refused to appear in any other film or television show that glorified violence. This included the role of Jimmy "Popeye" Doyle in The French Connection (1971). The role would earn Gene Hackman the Oscar for Best Actor. Boyle nevertheless played a ruthless gangster four years later in Crazy Joe (not a sequel) and also appeared in the violent drama Taxi Driver. "Joe" inspired the creation of other tough, working class characters in 70s films and TV shows, including the character of Archie Bunker on the TV show All in the Family.
In the 1980s, there were rumors that Peter Boyle might appear in a sequel to Joe. Citizen Joe, the sequel, would follow Joe as he tried to rebuild his life after spending 10 years in prison and would also deal with his grown up kids who held more liberal beliefs, as Arville Garland had. Cannon Films periodically took out ads for unmade sequels to Joe. In 1980, Cannon promised Joe II then, in 1985, announced the coming of Citizen Joe: The man has changed but the times have not. . . . He's back. The film never materialized.
Ten weeks before Joe was released in the United States, a real-life mass murder with similarities to the movie's climactic scenes occurred in Detroit, Michigan. On May 7, 1970, a railroad worker named Arville Douglas Garland entered a university residence and killed his daughter, her boyfriend and two other students.
During pre-trial deliberations, Judge Joseph A. Gillis saw Joe and strongly advised both the prosecution and defense teams to do the same. He then carefully screened each member of the jury pool and excluded any who had seen the movie. He also forbade any seated juror from watching the movie or discussing it with anyone who had seen it. Although he brought with him multiple weapons and extra ammunition, Garland received a light sentence.
Before and after sentencing, Garland received hundreds of letters from parents across the country who expressed sympathy with him. It was also reported that during the first weeks after his sentencing, he received no letters expressing outrage or condemnation of his actions.
Joe also featured an original soundtrack, introducing artists such as Exuma with the song "You Don't Know What's Going On", Dean Michaels' "Hey Joe" (not a version of the song made famous by the Leaves, Jimi Hendrix, and others), and other original songs by Jerry Butler and Bobby Scott.