Hilton was born in New York City and raised in Los Angeles. She is the daughter of Richard Hilton, a hotel heir of the Hilton family who works as a businessman in real estate and Kathy Hilton (née Avanzino), a former Actress and half sister of Kim and Kyle Richards. Hilton was named after her great-uncle, Conrad Nicholson Hilton, Jr. She is the second of four children: she has an older sister, Paris Whitney Hilton (born 1981), and two younger brothers, Barron Nicholas Hilton II (born 1989) and Conrad Hughes Hilton III (born 1994).

Hilton was raised Roman Catholic. She has Norwegian, German, Italian, English, Irish, and Scottish ancestry. Hilton graduated from Convent of the Sacred Heart, an all-girls Catholic school on the Upper East Side, in 2001. She took courses at Fashion Institute of Technology and Parsons The New School for Design but does not have a degree.

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 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 Stewart remains contracted, but Hilton has been replaced by Australian model Megan Maitland.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.

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 2010, Hilton launched a line of jewellery. The pieces are costume jewellery and in an art deco style, averaging around $200 per piece.

In 2011, Hilton began dating financier James Rothschild (born 1985), 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 (born July 2016) and Teddy Marilyn (born December 2017).

In August 2017, Hilton announced her collaboration with Tolani for a Mommy and Me capsule collection. The collection will be in stores Spring 2018.