The "Cool for the Summer" hitmaker belted out Whitney Houston's version of "I Will Always Love You" during the reception after the reality TV star and socialite and Carter Reum exchanged vows.
Paris revealed all on her website, stating Demi's performance brought "so much emotion and love" to the celebration.
"We made our grand entrance into the reception party, and had our first dance as Mr. and Mrs. Hilton-Reum," Paris wrote. "Carter and I aren't much of dancers (sic), but we've been practicing for weeks and I think we pulled it off! I loved Demi Lovato's performance of 'I Will Always Love You'. They were incredible. It brought so much emotion and love to the event."
Demi received a standing ovation for the performance, according to reports, while Bruno Mars' "Just the Way You Are" soundtracked the newlyweds' first dance as husband and wife.
"The reception was everything I wanted... chic, cute and fun...," Paris added. "I got to dance with my dad, and Carter had the most amazing dance with his mom."
She also revealed her sister, Nicky, gave an emotional speech about their childhood.
"We ended the night with dancing and raging to a DJ set," the socialite added. "It was the best day and night of my life. If I could do it all again I would in a heartbeat. I was incredibly happy being surrounded by so many loved ones and for everyone to be catching up and letting loose and celebrating."
Meanwhile, Kim Petras sang Hilton's hit "Stars Are Blind" at the ceremony and "I Can't Help Falling in Love With You" at the wedding, staged on the Bel-Air estate where Paris' late grandfather, Barron, lived.
"It was so surreal hearing Stars Are Blind being sung by one of my favorite singers now at our wedding, and knowing that as soon as it finished I would begin my walk down the aisle," Paris wrote. "She sang a stunning rendition of I Can't Help Falling In Love With You as I walked down the aisle that moved me so much. This was so surreal. It's like I had been dreaming of this moment my whole life."