The mountaineer fell ill at the last camp before the 8,156-metre summit and died as he was being taken down the mountain.
"We have confirmed that one person, a British national, has died between camp two and three. He went up to camp four but was not feeling well and was descending with our staff," said Iswari Poudel, head of the Himalayan Guides Nepal climbing agency.
The agency did not name the man.
"The body is still in the same area and we are getting permission from his family for further action."
More From This Section
At least 13 climbers and their sherpa guides have reached the top this month, while heavy snow has left other teams waiting at base camp for clear weather.
Last year 171 people summited Manaslu, according to the Himalayan Database, an archive of expeditions in Nepal.
Some leading operators running expeditions to Manaslu this month had a high number of cancellations by climbers concerned about overcrowding on the mountain, which has a very narrow summit on which only two people can stand at the same time.
Last year a Japanese climber died after slipping and falling off the summit while trying to take a photo of a teammate.