In 1942, journalist Manning (John Loder) arrives at an English air base to learn about the Free French who are fighting the Germans. Along with Captain Freycinet (Claude Rains), he watches as French bomber crews prepare for a raid. Manning's interest focuses on Jean Matrac (Humphrey Bogart), a gunner, and Freycinet describes Matrac's story:
Two years earlier, just before the defeat of France by the Germans, five convicts who escaped from Devil's Island are found adrift in a small canoe in the Caribbean Sea by the tramp steamer Ville de Nancy. These five men, Marius (Peter Lorre), Garou (Helmut Dantine), Petit (George Tobias), Renault (Philip Dorn), and their leader, Matrac, are rescued and taken aboard the French freighter commanded by Captain Malo (Victor Francen). Later, when confronted by Captain Freycinet, the five confess to being escaped convicts from the French prison colony at Cayenne in French Guiana. They had been recruited by Grandpère (Vladimir Sokoloff), a fervently patriotic ex-convict, to fight for France in her hour of need. To Grandpére, the inmates had recounted Matrac's troubles in pre-war France to convince the old man to choose Matrac to lead the escape. A crusading newspaper publisher, Matrac, being opposed to the Munich Pact, had been framed for murder to shut him up.
By the time the Ville de Nancy nears the port of Marseille, France has surrendered to Nazi Germany, and a collaborationist Vichy government has been set up. Upon hearing the news, the captain secretly decides not to deliver his valuable cargo to the Germans. Pro-Vichy passenger Major Duval (Sydney Greenstreet) organizes an attempt to seize control of the ship, but is defeated, in great part due to the escapees. When they reach England, the convicts join the Free French bomber squadron.
As Freycinet finishes his tale, the squadron returns from its mission over France. Renault's bomber is delayed, as Matrac is allowed to drop a letter over his family's house before returning from each mission. His wife Paula (Michèle Morgan) and their son, whom he has never seen, live in occupied France. Renault's bomber finally lands. It has been badly shot up, and Matrac has been killed. After the squadron bury him, Freycinet reads Matrac's letter to his son that had been unable to be delivered.
Passage to Marseille reunited much of the cast of Casablanca (1942), also directed by Curtiz, including Humphrey Bogart, Claude Rains, Sydney Greenstreet, Peter Lorre and Helmut Dantine. Other actors connected to both productions included Michèle Morgan who had been the original choice for the female lead for Casablanca; Victor Francen, Philip Dorn and George Tobias who are also featured.
Although exotic locales were called for, principal photography by cinematographer James Wong Howe, actually took place at the Los Angeles County Arboretum and Botanic Garden in Arcadia, California with additional location shooting in Victorville, California. Based on a Nordhoff-Hall novel, censors cut a scene in the foreign version that showed Bogart's character machine gunning German pilots.
Before Bogart began work on the film, pre-production had been underway for six months, but due to a conflict with Jack Warner over another prospective film (coincidentally) called Conflict (1945), his starring role as Matrac was in jeopardy, with Jean Gabin being touted as a replacement. Even when the issue was decided, Bogart's portrayal was hampered by marital difficulties and a lack of commitment to the project.
The flying sequences show the Free French Air Force (French: Forces Aériennes Françaises Libres, FAFL) using Boeing B-17 Flying Fortress bombers. The production took liberties with the actual bombing campaigns carried out by the Free French units, that primarily employed medium bombers such as the Martin B-26 Marauder. The use of the ubiquitous B-17 was due to its being recognizable to American audiences.
Bosley Crowther of The New York Times had a favorable review of Passage to Marseille, noting the film's "tough and tempestuous melodrama is something of a sequel, as it were, to the comment on Devil's Island which Warner was making five years ago. It is the studio's roaring rejoinder that a vicious and repressive penal code was still not sufficiently able to kill the love of home and freedom in French hearts."