Among the lots were a flamingo brooch, a bracelet in the form of a panther and a cigarette case which was inscribed with the route of a long European holiday the Duchess took with the Duke of Windsor, the former King Edward VIII.
Many of the items were gifts to the Duchess from the Duke, who gave up the thone to marry the former Wallis Simpson in 1937.
The sale of the 20 objects had been expected to generate around £3m but made £7,975,550.
The highlight of the auction was the onyx and diamond panther bracelet from 1952 which made £4,521,250. The piece had been expected to go for £1.5m and set a new record for the highest auction price for a work by Cartier.
The flamingo brooch, which is set with diamonds, rubies, sapphires and emeralds, made £1,721,250 against an estimate of £1.5m.
The Duchess's favourite bracelet - with nine small jewelled crosses representing significant moments in their relationship between 1934 and '44 - sold for £601,250.
A heart-shaped brooch topped by a crown with their initials in emeralds, sold for £205,250. It was commissioned by the Duke to mark the couple's 20th wedding anniversary in 1957, a date picked out in rubies at the base.
The flamingo, the panther, the bracelet and the brooch were among the Duchess's favourite pieces and dresses would be chosen to go with them when she travelled on the international society circuit between Paris, New York and Palm Beach.