The award-winning designer teamed her super mini cross-over dress with a thin gold belt, but as she walked the metallic accessory struggled to stay in place.
Having to pull it up on occasion, Stella, 41, nearly flashed a little more than she hoped for as she arrived at The Hoping Foundation's Rock On charity benefit at Cafe de Paris.
The colour purple suited McCartney's skin tone and reddish brown hair, but it couldn't distract from her slim legs as they emerged out the car that ferried her to the party.
Stepping out of the vehicle, the skirt of the dress rode up passed a thigh, coming close to revealing her private areas, but luckily the designer kept her legs closed the entire time to protect her modesty.
However as she walked around at points, Stella had to keep adjusting her gold belt so it would stay on her hip and not fall round her ankles.
Once in the party, her wardrobe malfunction took a back seat as she enjoyed the night with good friend Kate Moss and her rocker husband Jamie Hince.
The Kills guitarist lent his skills to Florence Welch during a special performance at the benefit to aid Palestinian refugee children, as did Patti Smith and Seasick Steve.
Clearly both the celebrity and public guests enjoyed the musical interludes, with the acts receiving standing ovations from Kate, 39, and Jamie, 44, but Stella stayed in her seat, opting to whoop instead.
Earlier in the night Brand, 38, had been on BBC Question Time, but he didn't even wait until the end credits were over to jump up and head to the charity bash in London.
Other guests on the night included Jeremy Clarkson, Hugh Grant, Jemima Khan and Noel Gallagher.
By Daily Mail Reporter