Dating from the late 19th to early 20th Century, the cushion-shaped sapphire displays a “saturated and vivid blue colour” and is estimated to be worth between £300,000-400,000.
It will be the first time the stone – which was formerly owned by a European noble family – has appeared at auction.
According to Bonhams, given its “remarkable size” together with the fact it comes from the mines of Kashmir, it is expected to “gain a lot of interest from buyers and collectors around the world” during its pre-sale previews in Geneva, New York and Hong Kong.
Emily Barber, director of jewellery at Bonhams UK, said: “Sapphires hailing from Kashmir are among the most highly-prized gems for serious connoisseurs.
“After the discovery of the mine in the high Himalayan mountain region of northwest India in 1881 the majority of mining activity took place during the following decade, after which the supply was essentially exhausted. This makes them extremely rare and highly desirable to collectors who want to add an important sapphire to their collection.”