The first of MGM's phenomenally profitable Jeanette MacDonald-Nelson Eddy musicals, Naughty Marietta takes several beneficial liberties with the libretto of the original Victor Herbert operetta. MacDonald plays an 18th-century French princess who escapes an arranged marriage by posing as a "cake girl," a mail-order bride sent to the New World to marry a colonist. En route, MacDonald and the other brides are captured by pirates, but are rescued by mercenary Eddy and his roistering companions. To avoid marrying some lowly farmer or frontiersman, simon-pure MacDonald intimates that she is a woman with a "history," which makes her attractive to the glitterati of old New Orleans. Only Eddy sees through MacDonald's feigned "naughtiness," and in the end claims her for his own. The most memorable of the Herbert songs retained for the film version of Naughty Marietta was "Ah, Sweet Mystery of Life", which remained one of Jeanette MacDonald's signature tunes ever afterward.
~ Hal Erickson, All Movie Guide