Marshall - nicknamed the Silent Assassin - impressively came through three bouts in Saint Petersburg and beat China's Li Qian to claim her biggest victory since winning Britain's first-ever women's boxing world title last year.
The pair appeared evenly matched with similar styles but Marshall's long jabs soon had the Chinese national champion struggling.
Elsewhere, British team-mate Jake Ball settled for silver after going down to Russia's Dmitry Bivol in their light heavyweight final.
World bronze medallist Natasha Jonas lost in the semi-finals of the women's lightweight division and Danny Dignum also fell one bout short of the final, losing to Ukraine's Vladyslav Voitaliuk in the men's middleweight class.
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