Harris, 41, turned to Twitter to announce news of his marriage to fellow actor David Burtka, 39, saying the couple wed in Italy over the weekend.
The exact location of the wedding was not announced, although actress Kelly Ripa told ABC News the ceremony was held in a rented castle.
Singer Elton John performed at the reception and director Pam Fryman officiated, People magazine said.
The couple announced their secret five-year engagement in 2011, less than a year after the birth of their twins. Just weeks ago Harris dispelled rumours that he had split from Burtka, posted a photograph of the happy couple on Instagram.
Gay marriage is banned in Italy, meaning the wedding will not be legally recognized in the country.