The 220cm (86.5in) item is said to have been discovered in Siberia in the 19th Century and carved in China.
It was purchased by a private buyer in New York in 2009 and was estimated to sell for up to £40,000 at an auction near Towcester, Northamptonshire.
The lot attracted bidders from around the world, but was bought by a private investor in London.
Humbert & Ellis Auctioneers listed the item as “extraordinarily rare and beautiful”.
Auctioneer Jonathan Humbert said: “This was a fair price for a thing of such utter beauty and we’re delighted with the outcome.
“The more you look, the more you see – it is a most remarkable and thoroughly beautiful piece of art.”
It features some 33 individuals figures, all with distinct faces and of Mogul influence, many bearing weapons, together with 20 horses, in an allegorical battle-story setting.
The tusk came from a woolly mammoth, a species which died out about 5,600 years ago, and was roughly the same size as modern African elephants.
It is exempt from the ivory ban, which currently only applies to products produced after 1947.