The female whale’s incredible journey began off the coast of Brazil and ended at Madagascar, almost 10,000km away.
The animal was photographed there two years after first being identified by researchers on Abrolhos Bank, Brazil, in August 1999.
Scientists do not know whether the whale’s epic trip was deliberate or the result of a navigational accident.
Humpback whales are known for long distance migrations, regularly travelling 5,000km between breeding and feeding grounds. However, these journeys generally take them north and south, not east or west.
Such a long trip between breeding areas is unexpected in a female, because it is more normal for male mammals to wander in search of mates.
The whale, known as Antarctic Humpback Whale Catalogue (AHWC) no 1363, was recognised by its distinctive markings.
It was originally one of a pair observed for about an hour off the Brazilian coast. The animal then disappeared until it was photographed on September 21, 2001, from a commercial “whale watch” tour vessel.
Researchers led by Dr Peter Stevick from the AHWC, College of the Atlantic, Bar Harbor, Maine in the US, said the distance travelled by the whale was the “longest documented movement by a mammal”.
They wrote in the Royal Society journal Biology Letters: “Movement of an individual between breeding areas separated by approximately 90 longitudinal degrees, a continent, an ocean basin and nearly 10,000km illustrates the ability of humpback whales to range across large portions of the globe.”
What led to the feat is uncertain, the scientists said.
Humpback whales tended to be attached to particular breeding areas and long-distance movement between different sites was rare.
This leads to restricted gene flow and relatively distinct breeding populations.
Previously recorded movements between humpback whale breeding grounds had been made by males.
The researchers said extreme long-distance travel by whales could result from exploring new habitats or a “navigational miscue”.