Hilton, 20, married Todd Andrew Meister, 33, at the Las Vegas Wedding Chapel, according a Clark County marriage license. A woman who answered the phone at the chapel declined to comment.
"Access Hollywood," which first reported the wedding, said older sister Paris Hilton and actress Bijou Phillips were present during the 2:30 a.m. ceremony Sunday.
The Hilton sisters were in town for a Stuff magazine party at the Palms Casino Resort, where they were joined by Meister and Nicole Richie for dinner late Saturday, resort owner George Maloof Jr. said.
Maloof, who confirmed the ceremony had taken place, said the couple gave no indication of their plans.
The group was joined in Las Vegas by friends including former 'NSync member Lance Bass, actress Tara Reid and actor Danny Masterson from "That 70's Show," according to "Entertainment Tonight."
Nicky Hilton, younger sister of "The Simple Life 2" star Paris Hilton, has dabbled in acting, appearing in "Wishman" in 1991 and presenting at MTV award shows.