In Paris, American producer Steve Canfield, Fred Astaire, wants Russian composer Peter Ilyitch Boroff to score his next picture. Three Soviet commissars Brankov, Peter Lorre, Bibinski, Jules Munshin, and Ivanov, Joseph Buloff, attempt to escort the composer back to Russia. To keep Boroff in Paris, Steve contests the composer's Russian citizenship by producing an affidavit disputing his parentage and insists it be resolved in court. Steve further convinces the commissars that Boroff's collaboration will earn them promotions in Moscow. Despite their initial resistance, the commissars consent to the collaboration.
Back in Moscow, Vassili Markovitch, George Tobias, becomes the new commissar of art. He sends Russian agent Ninotchka Yoschenko, Cyd Charisse, to retrieve Boroff from Paris. She meets the commissars in the hotel lobby. In their suite, Steve shows Ninotchka the affidavit and attempts to charm her with the locale, but Ninotchka insists that she will not be persuaded by the city's bourgeois.
Later that night, Hollywood actress Peggy Dayton, Janis Paige, arrives at the hotel, where several reporters interview her about her first serious role in an adaptation of War and Peace. The next morning, Steve escorts Ninotchka on a tour of Paris, alternating between boiler rooms and beauty salons. When they return to his hotel room, Steve sets a romantic mood with lower lights and music, but Ninotchka insists that romantic attraction is purely electro-chemical. > romantic attraction is purely "electro-chemical"
Steve and Ninotchka contrast their beliefs on romantic attraction, and after a waltz around the room, the two kiss.
Peggy walks into the room and insults Boroff, causing Ninotchka to leave. She tries to back out of the project because it's not a musical, to which Steve suggests she seduce Boroff into adapting his music to sound contemporary. At a costume fitting, Boroff, who is infatuated with Peggy, initially refuses to musicalize his compositions, but accepts the idea. Later that afternoon, Ninotchka locks herself in her room and dresses in Parisian lingerie. The same night, Ninotchka, dressed in a silky evening gown, joins Steve for a romantic evening. When Ninotchka returns to the commissars' room, they confess that Boroff's "Ode to a Tractor" is being rewritten into popular music for the film. Contrary to their suspicions, Ninotchka is delighted by the idea and dismisses them.
Alone with Steve, Ninotchka raves about Paris' beauty, convinced that love, not utilitarianism, leads to happiness. Months later, Boroff and the commissars, who have been saved from punishment by Ninotchka's report, visit her at her apartment. Ninotchka attempts to read Steve's letter, which has been so heavily censored that only the salutation remains. Soon after, Boroff, now fascinated with Western music, plays his new composition on the piano, prompting Ninotchka, the commissars, and the tenants to dance. Shortly after, Markovitch sends Ninotchka back to Paris to retrieve the commissars, who have been sent there to sell Russian films. When she arrives, the commissars take Ninotchka to their new Russian café, where Steve performs a top hat routine.
Back at the hotel room, Ninotchka states she will return to Russia that night. Steve arrives in the room, revealing that he wrote the anonymous report in order to get her out of Russia. He also reminds her of the marriage proposal contained in his censored letter. In love, Ninotchka rips up her plane ticket and embraces him while the commissars celebrate.
