It was one lot in a sale of high-end jewellery organized by auction house Sotheby's that raised a total of $95 million.
Josephine, who was queen consort of Sweden and Norway from 1844 to 1859, bore the same name as her illustrious grandmother, Josephine de Beauharnais (1763-1814) — the first wife of Napoleon Bonaparte.
The necklace, which includes seven pear-shaped pearls, had an estimated value of between $800,000 and $1.5 million.
Wednesday's sale also included several pieces from the collection of Greek financier Dimitri Mavrommatis with an estimated combined value of $20 million, which sold for $27.8 million.
The star of the collection was an 8.62-carat Burmese ruby set in a ring known as the Graff Ruby, acquired by London jeweller Laurence Graff in 2006 for $3.6 million.
Graff sold it to Mavrommatis for an undisclosed sum, and it garnered $8.6 million on Wednesday.
A rare sapphire and diamond ring from the collection sold for $6 million.