The 74-year-old was on a tour of the Caribbean which left New York on Thursday, reports the Press Association.
The alarm was raised when the ship was around 100 nautical miles south east of Atlantic City in New Jersey, and the US Coast Guard scrambled a plane and helicopter to help search for her.
A company spokesman said: “It is with sadness we can confirm that after a comprehensive search, working with all relevant authorities, Queen Mary 2 has halted the search for a missing guest, presumed overboard.
“The ship left New York on December 22, on a 12-night Caribbean itinerary. Cunard’s care team is offering every support to the family.
The Coast Guard had launched a C-130 fixed wing plane and an HH-60 Jayhawk helicopter to scour the sea, searching an area of almost 400sq nautical miles, but they have now returned to land.
Petty Officer David Micallef told the Press Association the woman was reported missing between 1am and 3am US time on Friday, (8pm to 10pm on Thursday, British time).
The Queen Mary 2, based in the port of Southampton, was built in 2003 at a cost of £700 million and launched the following year.
The luxury ship was renovated earlier this year and boasts suites, state rooms and the “largest library at sea”, with 8,000 books, according to the Cunard website.