Colleagues on the Cunard flagship spent five hours looking for the man as the vessel made its way from Southampton to Halifax, Canada.
But a spokeswoman for operator Cunard said the search had now been called off.
She said: “A search was carried out for a missing crew member on Queen Mary 2. It has been clearly established that the crew member went overboard earlier this morning.
“The ship was off the coast of Newfoundland and in association with local authorities, it carried out an extensive search of the area in which he went overboard but unfortunately there were no sightings.
“Having discussed this with experts ashore there is no possibility that the crew member could have survived this long in the water and we therefore have to presume that he died in the water.
“Our thoughts and prayers are with his family, which is being informed, as well as friends and his colleagues on board.”
Passenger Allan Bonner said there were numerous on-board announcements for a man called Favio Ordenes, believed to be a 26-year-old chef, before the search began.
Mr Bonner said: “As the ship appeared to be approaching the Grand Banks, the captain Kevin Oprey made a dignified announcements saying we’re going back to the spot that Mr Ordenes was first thought to be missing. About five-to-six hours later, we were searching the ocean.
“The captain has made a series of professional, calm announcements about what’s going on.
“Some crew say they’ve never heard of losing a crew member. Some memories go back 30 or so years.
“The rocking of the usually calm ship was a signal that something abnormal was going on.”
Mr Bonner said passengers were also attempting to search for the missing man by peering over the railings, although all efforts to find him were hampered by dense fog.