The non-denominational ceremony was attended only by the bride and groom, who were both barefoot and wearing white, the magazine said on its Web site.
"We didn't want to wait another day to get married," People quoted Spelling as saying.
Added McDermott: "I've never had as much of a desire to get married and make a woman my wife as I've had with her. The feeling is overwhelming. We're soul mates."
Spelling, 32, and McDermott, 39, met last year while filming the TV movie "Mind Over Murder."
Spelling was married at the time to actor-writer Charlie Shanian, who filed for divorce in October, a little more than a year after marrying the former "Beverly Hills, 90210" star. The divorce was finalized last month.
McDermott filed for divorce from his wife of 12 years, Mary Jo Eustace, in September.
McDermott proposed to Spelling on Christmas Eve in Toronto.
Spelling, who is the daughter of producer Aaron Spelling, is starring as a fictionalized version of herself in VH1's "so noTORIous."
A call and e-mail to her publicist were not immediately returned.