The pair, together for 28 years, tied the knot at the Beverly Hills Hotel, Entertainment Tonight reported.
The ceremony was attended by their son Nick, 22, and daughter Sophie, 19, and took place outside on the hotel's crystal lawn, People magazine reported.
Tweed, 54, wore an ivory Priscilla of Boston dress and walked down the aisle holding a bouquet of ivory garden roses, according to the magazine.
The pair exchanged vows they wrote themselves, with their 400 guests cheering when Simmons said "I do" to his partner.
In a fitting choice of song, their daughter, who was also the maid of honor, performed Etta James' "At Last" for her parents' first dance.
The sharp-tongued and spandex-wearing Simmons proposed to Tweed on his A&E reality show, "Gene Simmons Family Jewels," earlier this year. The show followed their therapy sessions after Simmons' claim that he has slept with nearly 5,000 women, with the rock star adding in a later interview that "a lot of them didn't get a lot of sleep."
But it was not all smooth sailing for the couple. After the proposal was aired, Tweed admitted that there was a "slim chance" of them really getting married. She told People magazine, "You're seeing this happy family ... but in my heart, I am dying" -- and added that she needed commitment for the relationship to work.
Last week, just days before the wedding, Simmons told Entertainment Tonight he was ready to "grow up" and settle down, saying that "28 years is long enough to go out on a date. Be afraid, be very afraid."
He added, "It is time for me to grow up. I'm 62. I've been doing a lot of wacky stuff for an awfully long time -- the band, the thing, traveling around the world and all that."
Tweed also told Entertainment Tonight on Wednesday that her soon-to-be husband did not promise to be faithful to her.
"I will do my best. We're going to have to wait," Simmons replied.
The wedding will be featured on the couple's reality show Tuesday.