In 2001, Němcová appeared on British television series Absolutely Fabulous. On 3 June 2004, she was one of the telecast judges during the 53rd annual Miss Universe competition in Quito, Ecuador. In 2007, she was the host of TLC’s A Model Life. On 7 July 2007, she was a presenter at the American leg of Live Earth. Němcová was a contestant on season 12 of Dancing with the Stars with dance partner Dmitry Chaplin, reaching the 4th week before being eliminated.

Němcová gained attention outside the fashion industry after featuring on the cover of the 2003 Sports Illustrated Swimsuit Issue, from a shoot in Barbados by Walter Iooss. She also appeared in the 2002, 2003, 2004, 2005 and 2006 editions. She was the object/subject of Joanne Gair’s body painting work. In January 2015 Němcová replaced Abbey Clancy as the face of Ultimo underwear. She also serves as the global face of Chopard.

On 26 December 2004, Němcová was in Khao Lak, Thailand, with her main photographer and boyfriend, Simon Atlee, when the 2004 Indian Ocean earthquake and tsunami struck. Atlee drowned and Němcová suffered a broken pelvis and serious internal injuries, but she managed to hold on to a palm tree for eight hours until she was rescued by Thai civilians and airlifted to an inland hospital nearby.

In 2005, Němcová published her autobiography Love Always, Petra ( ISBN 0446579130).

Her autobiography, Love Always, Petra, was released in 2005 from which 100% of the proceeds were donated towards helping children affected both by the 2004 tsunami in Thailand and ongoing natural disasters worldwide.

In 2005, Němcová founded the Happy Hearts Fund (HHF), a charitable organization and campaign formed after the tsunami of 2004. The main mission of Happy Hearts Fund has been to rebuild and renew schools affected by natural disasters. As a result of programmes run by the Happy Hearts Fund, 176 schools have been rebuilt world-wide in 10 countries including Thailand, Indonesia, Haiti, Nepal, Peru, Mexico and The Philippines. Němcová has been heavily involved on an every day basis since establishing the Happy Hearts Fund, helping to establish long term strategies, as well as outlining the vision which has led to the organisations long term success. Her personal experience during the 2004 Boxing Day Tsunami gave her a deep understanding of the power of Mother Nature, allowing her to connect with those in need, bolstering the success of her work through the organisation. In late 2017, the Happy Hearts Fund merged with fellow non-profit organisation All Hands Volunteers to create All Hands And Hearts – Smart Response. As a result, Němcová now acts as co-founder and vice chair of All Hands And Hearts alongside All Hands Volunteers founder David Campbell.

Glamour magazine awarded Němcová a “Survivor Award” in 2005 for her charity work following her tsunami ordeal.

In June 2012, she was designated by president of Haiti Michel Martelly and Prime Minister Laurent Lamothe as Ambassador-at-Large for Haiti for her work with Happy Hearts Fund.

She was briefly engaged to English actor Jamie Belman before the couple ended their relationship in 2012.

In May 2014, Němcová told People that she was dating the Prime Minister of Haiti, Laurent Lamothe. but as of 2015 they were no longer together. In 2017, she became engaged to investment banker Alejandro Grimaldi before the pair called off their engagement in December 2018.

In 2017, Petra was appointed by the UNISDR as a Disaster Risk Reduction Champion and Tsunami Awareness Advocate.

In 2019, Němcová married French-Venezuelan entrepreneur Benjamin Larretche in Sedona, Arizona. They announced in September 2019 that they are expecting their first child. They welcomed their first child, a son, on 15 November 2019. He was born at 34 gestation and spent the first weeks of his life in the NICU.