Picking up two or three years after where the original left off, narcotics officer Jimmy "Popeye" Doyle (Gene Hackman) is still searching for elusive drug kingpin Alain Charnier (Fernando Rey). Orders from his superiors send Doyle to Marseille, France, to track down the criminal mastermind and bust his drug ring. Once in France, Doyle is met by Inspector Henri Barthélémy (Bernard Fresson), who resents his rude and crude crimefighting demeanor. Doyle then begins to find himself as a fish out of water in France, where he is matched with a language he cannot understand. Doyle is shown round the police station where he finds his desk is situated directly outside the toilets. He tells Barthélémy that he is not satisfied with this positioning and hopes it is not a joke at his expense. Barthélémy informs Doyle that he has read his personnel file and is aware of his reputation and especially hopes he has not brought a gun with him as it is strictly forbidden in France for visiting police officers from other countries to carry firearms.
Doyle continues to struggle with the language and tries to order drinks in a bar. He eventually makes himself understood, befriending a bartender while buying him drinks and they eventually stumble out of the bar together at closing time. Determined to find Charnier on his own, Popeye escapes from his French escorts. While Doyle watches a beach volleyball match, Charnier sees him from a restaurant below. Charnier sends his henchmen to follow Doyle through the town, where they capture him and take him to a hotel for interrogation.
For several weeks, Doyle is injected with heroin in effort to force him into capitulation. Scenes of his growing addiction follow, including one in which an elderly lady (Cathleen Nesbitt) visits him in his befuddled state. She talks to him, declaring herself to be English, and saying that her son is "just like" him, while stroking his arm. Initially she seems compassionate to his plight, but a change in the camera angle reveals her 'track' marks and that she is slowly removing his watch.
Barthélémy has sent police to search for Doyle and, as the raids close in on where Doyle is detained, he is dumped barely alive but addicted in front of police headquarters. Scenes of resuscitation and drug withdrawal follow. In his effort to save both Doyle's life and his reputation, Barthélémy immediately quarantines Doyle in the police cells and begins his cold turkey withdrawal from the heroin. Supervising his recovery, and at his side with both emotional support and taunts questioning his toughness, Barthélémy ensures Doyle completes the cycle of physical withdrawal. When he is well enough to be on his feet, Doyle starts back on the road to regaining his physical fitness. He searches Marseilles and, finding the hideout/drug warehouse he was brought to, he sets it on fire. He breaks into a room at the hotel and finds Charnier's henchmen, whom he interrogates as to the whereabouts of Charnier. Doyle is joined by Barthélémy and other inspectors who engage Charnier's henchmen in a gun battle in a dry dock, which results in water from multiple spillways pouring out. The henchmen and inspectors are killed but Doyle rescues Barthélémy. The following raid on Charnier and his henchmen is successful, but Charnier escapes. Doyle, in a foot chase of Charnier, who is sailing out of the harbor on his yacht, takes his gun out of his holster, calls Charnier's name, and finally shoots him dead.Gene Hackman as Det. Jimmy "Popeye" Doyle
Fernando Rey as Alain Charnier
Bernard Fresson as Henri Barthélémy
Philippe Léotard as Jacques
Ed Lauter as General Brian
Charles Millot as Miletto
Jean-Pierre Castaldi as Raoul Diron
Cathleen Nesbitt as The Old Lady
Reine Prat as The Girl on the Volleyball Beach
John Frankenheimer had lived in France for a number of years when he agreed to make the film:
I like the script, I like the characters, I like the Hackman character in France and not speaking a word of French. It's a very difficult film because we want in no way to rip off the first one, which is one of the best films I've ever seen. I want to make a movie that stands on its own as a movie.
Frankenheimer also admitted he made the film in part because of the financial failure of The Impossible Object. "I want to make pictures that one sees," he said. "There's a great public out there and you have to reach them; otherwise you're not in the movie business."
The music was composed and conducted by Don Ellis, who returned from the original film. A soundtrack CD was released by the Film Score Monthly in 2005 and paired with the music from the first film.
The film has received generally positive reviews. Review aggregate Rotten Tomatoes reports that 76% of critics have given the film a positive review based on 21 reviews with an average score of 6.6/10.
Roger Ebert of the Chicago Sun-Times gave the film two and a half out of four stars and said that "if Frankenheimer and his screenplay don't do justice to the character (of Jimmy "Popeye" Doyle), they at least do justice to the genre, and this is better than most of the many cop movies that followed The French Connection into release."
Vincent Canby wrote in his review in the New York Times, "Popeye is a colorful and interesting — though hardly noble — character, and when the Marseilles drug people kidnap him, forcibly create a heroin habit in him, and then release him, you have a very special kind of jeopardy that the film and Mr. Hackman exploit most effectively".
The film earned North American rentals of $5.6 million, surpassing its $4.3 million budget.
Empire considered French Connection II to be the 19th greatest film sequel in 2009.