Montag, 22, and Pratt, 25, wed in front of more than 200 guests Saturday at 4 p.m. at the Westminster Presbyterian Church in Pasadena, Calif., Usmagazine.com has confirmed. (A skywriter above the church wrote "Spencer Loves Heidi" numerous times in the clouds before the ceremony.)
Montag -- who was draped in close to $1.2 million in Neil Lane jewels -- wore a custom-made, $19,000 Monique Lhuillier dress.
Her sister, Holly, served as maid of honor. Pratt's sister, Stephanie, was also a bridesmaid in the ceremony.
Pratt wore an Ermenegildo Zegna suit, as did all of his groomsmen.
His niece, Ava, was the flower girl.
Heidi's father walked her down the aisle.
Both Pratt and Montag didn't shed any tears during the ceremony, a guest tells Us, They also didn't say their own vows; the minister did.
In addition to Pratt's family, all four of Montag's parents were present - including her mother, Darlene Egelhof, who initially opposed the couple eloping in Mexico last November.
Lauren Conrad, who initially said she would not attend, had a change of heart and showed up, along with Brody Jenner and girlfriend Jayde Nicole, Audrina Patridge, Frankie Delgado and Lauren "Lo" Bosworth. The ceremony was filmed for their MTV show.
Music producers David Foster and Cathy Dennis -- who worked with Montag and also produced Katy Perry's "I Kissed a Girl" -- were also present.
On Friday, the couple held a rehearsal dinner at Wolfgang Puck's Beverly Hills hotspot, Cut.
Their wedding Saturday was wholly different from the casual ceremony they had in Cabo San Lucas, Mexico, last November.
Pratt said it was "totally spur of the moment" when he and Montag exchanged vows with $8 rings they picked up on their trip.
Still, Montag told Us, "The minute we said our vows, I couldn't stop crying."
Outraged that they secretly eloped, Montags mother told Us Weekly at the time that she gave their marriage "six months."
Montag and Pratt planned to make the Mexican wedding official with a trip to the Beverly Hills courthouse but Pratt had a change of heart at the last minute. Montag, he said, always wanted a traditional wedding with family and friends and a simple, courthouse ceremony didn't feel right.
"I just want to give you the wedding of your dreams that you have been talking about for three years," he said on The Hills season 4 finale last December. "I'll deal with it. It's worth it to be with you the rest of my life. We'll do it the way you want, I'm sorry, I love you so much."
Despite the controversy over the couple, their pal Patridge tells Us the two are made for each other.
"They've been together for so long, and they are two peas in a pod," she tells Us. "I mean, they are Heidi and Spencer! I can't see either of them with anyone else. Heidi loves him."
Photos: Spencer and Heidi