The Galaxy Gear allows users to access emails, texts and even make phone calls - without touching their mobile.
It works via a Bluetooth connection with the new Samsung Galaxy Note 3 phone.
Presenter Jonathan Ross, former track cyclist Victoria Pendleton and model Donna Air were among the stars who attended the preview party at the Radio Rooftop Bar in central London.
Ellie Goulding performed at the event, while Daisy Lowe was the DJ.
The party was hosted by Vernon Kay, who joked that he was a fan of the smartwatch, which also features a camera, because "everyone wants to be James Bond".
Simon Stanford, vice president of Samsung UK, said: "We certainly believe this is the first truly mobile wearable technology in terms of the interaction you can get with this device.
"Anything from making calls, receiving texts, there's your calendar, the pedometer, a stopwatch, and it's the most accurate time you'll ever get.
"This particular product is going to change the way the connected world is going to start moving."
He added: "It's a groundbreaking product. The wearable technology piece with the Note 3 is a real innovative combination of products in the market. It's pretty unique."
The recommended retail price for the Gear is £299, while the Note 3 costs around £599.
Goulding, who wore a tight-fitting white sparkly dress, performed hits including Your Song and Starry Eyed.
Singer Sophie Ellis-Bextor, boyband Union J, socialite Peaches Geldof and JLS member Oritse Williams also attended the champagne-fuelled bash.