Born 15 December 1986 in Severodonetsk, Onopka moved to the Ukrainian capital, Kiev, in 2001. While there, she was spotted by a foreign scout at the age of 15 and thus began her career as a model.
In 2005, Steven Meisel photographed Onopka for the Prada and Dolce & Gabbana fall ad campaigns, sparking a booking frenzy thereafter and he then photographed her for two covers of Italian Vogue. In September 2005 she debuted by closing Marc by Marc Jacobs show in New York and also opened the Dolce & Gabbana and Karl Lagerfeld shows. In 2006 Steven Meisel photographed her for Calvin Klein and Dolce & Gabbana campaigns, Mert Alas and Marcus Piggot photographed her for a Louis Vuitton campaign and Juergen Teller photographed her for Yves Saint Laurent. The same year Onopka became the face of Lanvin, replacing Lily Donaldson. Onopka has graced the cover of i-D, Numéro, Harper's Bazaar, L'Officiel, Allure Russia, Elle Ukraine, Glamour Russia and the Portuguese, Japanese, and French editions of Vogue. On the runway, Onopka has walked for designers including Chanel, Gucci, Anna Sui, Balmain, Dolce & Gabbana, Marc Jacobs and Isabel Marant.
During the New York's Fall/Winter 2007 fashion shows Onopka was noticeably absent, because she was shooting the Shiseido Spring/Summer 2007 campaign. However, at the start of Milan Fashion Week she was back in full force walking for shows including Burberry, Jil Sander, Gucci and Dolce & Gabbana.
Throughout her career Onopka has also appeared in advertising campaigns for Prada, Lanvin, ck Calvin Klein, Yves Saint Laurent, Louis Vuitton eyewear, Shiseido, Gucci, Gucci Eau de Parfum II, Max Mara, Hugo by Hugo Boss, Hugo by Hugo Boss eyewear, Etro and Emilio Pucci eyewear.
In September 2017, Onopka returned to the runway and opened the Natasha Zinko show at London Fashion Week.
Onopka was quoted in Teen Vogue saying this about her family: "My mother collects tear sheets of everything she sees me in." And about her father: "My father was in a rock band when I was growing up, so he's used to the spotlight. I like to sing, too." On November 15, 2011, Onopka married 29-year-old businessman Mykola Shchur.