Both Hungary and Croatia claimed that the silver had been unofficially excavated on their respective territories and illegally removed - and that it should, under their own and American laws, be returned to the country it came from.
Croatia and Hungary's lawyers indicated they were likely to appeal against the verdict.
The Marquess, 47, has sat through the whole of the seven-week trial. He told the court that he paid dollars 11m ( pounds 5.2m) to acquire the silver between 1982 and 1987, in collaboration with the late Peter Wilson, a former chairman of Sotheby's, and a London art dealer.
Pre-trial proceedings revaled that when Lord Northampton turned to Sotheby's in 1989 to sell the silver he was hoping to get pounds 60m for it, though Sotheby's own valuation was about pounds 40m.
The treasure was on display in the United States in 1990 prior to being taken to Switzerland for sale when a claim for its ownership was laid before the New York Supreme Court. Croatia and Hungary later joined the action.
Lord Northampton said he was 'delighted' with the court's decision yesterday and now hoped to sell the silver.
His British lawyer, Ludovic de Walden, said that they would be pursuing an action against Allen and Overy and Peter Mimpriss, the solicitors who acted for Lord Northampton's interest over the Sevso treasure until 1990.
Mr de Walden said that he would also be investigating the status of a Scotland Yard inquiry into the origins of the silver, which has not hitherto led to any prosecutions.Reuse content