Moore, 42, and Kutcher, 27, exchanged vows in front of 100 guests, including Demi's daughters, actress Soleil Moon Frye and her husband Jason Goldberg (who is Kutcher's Punk'd producing partner), as well as other close friends and family.
"They are so happy together," says a source close to the couple.
The ceremony came together at the last minute; final preparations were completed within 24 hours. "It was a Kabbalah ceremony," according to a source.
The couple's rep declined to comment.
This is the first marriage for Kutcher and the third for Moore, whose previous unions – to rock musician Freddie Moore (1980-84) and to actor Bruce Willis (1987-2000) – ended in divorce.
Kutcher and Moore initially met at a casual dinner in New York City in 2003. After the That '70s Show star began dating Moore that May, he quickly carved out a place in the lives of her three daughters by Willis – Rumer, 17; Scout, 14; and Tallulah, 11 – who came to embrace Kutcher as a third parent, affectionately calling him MOD, short for "My Other Dad."
"We talk about everything," said Kutcher of his close ties to the young women. "It's amazing."
In February, Moore and Kutcher – who spend most of their time in Los Angeles – slipped away to Cabo San Lucas, Mexico, to celebrate Valentine's Day at a resort overlooking the ocean. The getaway sparked rumors that Kutcher proposed (wrong) and that the duo eloped (wrong again).
They've also long fended off rumors that Moore was pregnant. "Why am I the last person to find out everything?" Kutcher joked to reporters last spring, as British tabloids announced that Moore was to be a mom again. "I'm going to be a daddy? God, no one tells me anything."
At the time, Moore's rep denied the pregnancy report but acknowledged: "Having another child is something Demi would like to do." During an appearance on David Letterman, Kutcher also said he "absolutely" wants to have kids.
As for the key to the couple's blissful bond, they curb their negative emotions – a basic tenet of the pair's Kabbalah beliefs – and they are also always up-front with each other. "When I'm putting up a front, she calls me on it," Kutcher told Oprah Winfrey in April. "And I call her on her crap."
Also on Oprah, Kutcher expressed his happiness with Moore saying: "I love being with her. She makes me a better person."
Eric Charbonneau / BEI