The rough cut of the film ran four hours. In reducing it to two hours, several actors were cut, including Ruth Warrick. She does appear briefly in the restored 133-minute version.
During filming in Paris in October of 1946, the government drained the Seine to remove live bombs and inspect the foundation of a bridge. This resulted in the crew having to improvise the river in the background of some shots.
Irwin Shaw spent five months writing a screenplay, but then quit after director Lewis Milestone wanted him to add a love story. Milestone rewrote the script, which was preferred by the studio and Ingrid Bergman.
The additional scenes written for Charles Laughton were filmed in New York City in November 1946, because Ingrid Bergman was then starring in a Broadway production of "Joan of Lorraine".
Michael Chekhov was originally cast in the role of Ivon Haake, but had to leave after he became ill. The script was rewritten to beef up that part for his replacement, Charles Laughton.