The ceremony reportedly took place in Paris, where the two spent a week at the Hotel Ritz and were photographed at the Place Vendôme wearing matching berets.
The couple, who have been together for about eight years, have a daughter, Olive, born in 2007.
"We did it - we're married!" Fisher told friends in an e-mail, reports Women's Day. "It was the absolute best day of my life and in so many beautiful moments I missed you all so much. I thought of you as everything was happening, but Sacha and I wanted no fuss - just us!"