No details regarding when or where the couple exchanged vows were immediately available.
The couple met on the set of the 2010 film "Black Swan," for which Portman earned an Oscar for Best Actress. She and Millepied are the parents of an infant son together.
They sparked marriage rumors when they attended Sunday's Oscars ceremony wearing what appeared to be matching wedding rings.
"I designed the rings worn by Benjamin Millepied and Natalie Portman," jeweler Jaime Wolf told Us. "They were made with recycled platinum and conflict-free diamonds."
The celebrity news Web site said Portman's publicist and manager did not reply to its requests for comment.
Attkisson leaves CBS News, reportedly over network's 'liberal bias'
Duggar sisters unveil Christian dating rules in new book