Krupa was born in Warsaw, Poland on 23 April 1979. She was raised Roman Catholic. She has a younger sister, Marta, who is also a model. Krupa moved to Illinois with her family at the age of five. In Chicago, she attended Mary Lyon Public School, followed by Steinmetz High School.

On 2 December 2009, animal rights organization PETA released a print ad campaign for dog adoption featuring Krupa as an angel floating in a Catholic church filled with dogs, and holding a cross covering her breasts and genitalia. Krupa had previously appeared in a PETA ad campaign against the use of natural fur. In an April 2009 cover story with Aventura Business Monthly, Krupa said she was first motivated to promote PETA when she saw video of animals being skinned alive for their fur in China. She posed covered in body paint for PETA in 2015, this time for their campaign to boycott SeaWorld. She also founded an animal rescue group, Angels For Animal Rescue, with her friend Gabi Gutierrez.

Since 2010, Krupa hostes and severs as the head judge on the Polish version of Top Model.

After several years of dating, Krupa became engaged to nightclub owner and businessman Romain Zago in 2010. They married on 13 June 2013 in Aviara, Carlsbad, California. On 10 July 2017, she filed for divorce. The divorce was finalized on 17 August 2017. On March 25, 2018, she announced her engagement to Douglas Nunes on Instagram. They married on 4 August 2018 in a private ceremony at the Benedictine Abbey in Kraków, Poland. The couple announced they were expecting their first child together. They welcomed daughter Asha-Leigh Nunes on November 2, 2019.

Krupa has appeared on magazine covers including FHM, Inside Sport, Stuff, Steppin’ Out, Shape and Maxim, in which she was named the Sexiest Swimsuit Model in the World. Maxim named her #55 in its 2011 Hot 100 ranking of the world’s hottest women. She was voted German Maxim’s Model of the Year 2004–2005. Krupa has also appeared twice on the cover of Playboy and graced the covers of South African GQ and the Polish editions of Cosmopolitan, InStyle, Glamour and Grazia.

Joanna Krupa was the subject of an article on 29th November 2016 on the website Women Fitness.