The Queen Mary 2 cruise ship called off the search for a crew member late Saturday after he went overboard off the coast of Newfoundland.
Colleagues on the Cunard vessel spent five hours looking for the man as they made their way from Southampton to Halifax, Canada.
A spokeswoman of Cunard cruise line said the search has now been called off. The company has not released the name, occupation or nationality of the missing crew member, who is not thought to be British.
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."
The ship was travelling from Southampton to New York. It is due to stop in Halifax, Nova Scotia, on Monday.
Christened in 2004, the ship is 345 metres long, has 19 decks and carries 2,620 passengers.
Described by Cunard as "wonderfully grand," the ship boasts the largest dance floor at sea, a luxurious 3D cinema, a planetarium and a classical music venue.