Born in Marseille,[1] France, she was the daughter of Henri Louis Firmin Clair Simon, a French Jewish engineer and airplane pilot in World War II who died in a concentration camp, and Erma Maria Domenica Giorcelli, an Italian housewife.

[3] After being spotted in a restaurant in June 1931, Simon was offered a film contract by director Victor Tourjansky, which ended her plans to become a fashion designer.

[2] She made her screen debut in Le chanteur inconnu (The Unknown Singer, 1931), and quickly established herself as one of the country's most successful film actresses.

[3] It was usual for foreign actresses to receive months of preparation before working, but Simon was given only a few weeks of English lessons before she was told to report on set.

Although it was reported that she withdrew due to illness, it was later revealed that Zanuck fired her after twelve days of shooting because of her temperamental behavior, which displeased the film's director Frank Lloyd.

[5] She admitted, though, that in the early stage of production she was temperamental, insisting that she was inspired to behave that way after a conversation with Marlene Dietrich, who told her that "a star is only as important as she makes herself out to be.

"[7] She dismissed any further claims of her being rude or difficult to work with, explaining to the press that she was initially not used to the American lifestyle, which was in her view more extroverted than the French way of living.

She shared the female lead with Janet Gaynor, Loretta Young and Constance Bennett, some of whom objected to the large number of scenes that Simon was getting.

[12] Failing in finding her appropriate roles, the studio allowed her to go on an eight-week vacation to France, and following her return in June 1937, she was assigned to Suez (1938), but the project was shelved and she was eventually replaced.

With the outbreak of World War II, she returned to Hollywood and worked for RKO Radio Pictures where she achieved her greatest successes in English language cinema with The Devil and Daniel Webster (1941), Cat People (1942) and The Curse of the Cat People (1944); the latter two formed part of the horror film series produced by Val Lewton.

At the time, due to her relative obscurity in the United States, Simon generated a series of apocryphal rumors about her origins, such as that she was the love child of Marion Davies and William Randolph Hearst, and that she had been a Paramount stock player from Salem, Oregon.