In 2004, Hilton launched her own clothing line. She also designed a line of handbags for Japanese company Samantha Thavasa. In 2007, she started her second line, Nicholai, at a higher price point. Nicholai held its fashion show for the spring/summer 2008 season on September 9, 2007, in New York City during Mercedes-Benz Fashion Week. In 2014, Hilton launched a 10-piece collection with eLuxe. She designed each piece as a reflection of her personal style and named all products for the women in her family, who embody the style of each piece. In 2010, Hilton launched a line of jewelry. The pieces are fashion jewelry and in an Art Deco style, averaging around $200 per piece. In 2015, she launched a capsule collection of handbags as part of a collaboration with Linea Pelle. Hilton said she was approached by Linea Pelle "to make a capsule collection and I really wanted to have it be classic. As in I didn't want to make these super trendy bags that would be out of style next season." In August 2017, Hilton announced her collaboration with Tolani for a Mommy and Me capsule collection. The collection launched in stores in spring 2018.. In 2019 Hilton launched a second collection with Tolani inspired by her travels. In February 2019, Hilton announced her first footwear collection in partnership with French Sole.. The line, known as Nicky Hilton x French Sole, officially launched in September 2019.
Model
In 2005, Hilton was the face of Australian underwear line Antz Pantz alongside Kimberly Stewart. Stewart remains contracted, but Hilton has been replaced by Australian model Megan Maitland. Around this time, Hilton modeled for the cover of Lucire for its New Zealand and Romanian editions.
Other ventures
In 2006, she entered a partnership to open two Nicky O Hotels, the first in Miami and the second in Chicago. That same year, Hilton sued her partner in Federal Court in Los Angeles for damages and to seek an injunction against his use of the name. On February 12, 2007, Hilton was sued for breach of contract by her partners. In 2014, Hilton published her first book, 365 Style, published by Harlequin, a subsidiary of HarperCollins. In 2015, Hilton collaborated with Smashbox, the cosmetic brand owned by Estée Lauder Companies, to create a cosmetic line consisting of three limited-edition cat-inspired makeup kits.
At 2:30 a.m. on August 15, 2004, Hilton married childhood friend and businessman Todd Meister at the Vegas Wedding Chapel in Las Vegas, Nevada. The marriage was annulled less than three months later, with Hilton and Meister explaining they traveled apart often and had married "on a whim". In 2011, Hilton began dating financier James Rothschild, a member of the Rothschild family and only son of Amschel Rothschild, after being introduced at James Stunt and Petra Ecclestone's wedding. On August 12, 2014, while on vacation at Lake Como in Italy, Hilton became engaged to Rothschild. On July 10, 2015, the couple married at The Orangery in Kensington Palace Gardens in London, England. Hilton wore a $77,000 Valentino Haute Couture gown. Her sister, Paris, served as maid of honor. The couple honeymooned in Botswana. They have two daughters: Lily Grace Victoria Rothschild and Teddy Marilyn Rothschild.