The model, who had dumped Hefner, 86, in 2011, opted for a small ceremony on New Year's Eve at the Playboy Mansion.
"Today is the day I become Mrs Hugh Hefner. Feeling very happy, lucky, and blessed," Harris, who was Playboy's Miss December 2009, tweeted earlier in the day.
She has changed her name on Twitter to "Crystal Hefner."
Hefner, who has two failed marriages behind him, was scheduled to marry Harris in June 2011 but she dumped him only five days before they were to be married.
"After much deep reflection and thought I have decided to end my engagement with Hef. I have the utmost respect for Hef and wish him the best going forward," Harris had said in a statement at that time.
Things later turned ugly for the couple as Harris started sharing ugly details about their sex life.
Despite their war of words, the couple reunited earlier this year.
"Yes, Hugh Hefner and I are back together. Yes I am his #1 girl again. Yes we are happy. Hope that clears up any confusion! XO," Harris tweeted later.
Hefner was previously wed to Mildred Williams and Kimberley Conrad and has two children with each of his ex-wives.
It's the first marriage for Harris, who recently opened a lingerie store, Femme Fatale, in Studio City, California.
