The 'Price Tag' singer, 25, flashed a whole lot of cleavage when she attended Capital Rocks - a fundraiser organised by Capital FM and Help A Capital Child.
With her newly-dyed black hair in a sleek pixie crop, and her make-up designed to look natural, Jessie J looked pretty as a picture in her silk floor-length gown.
The former Voice judge was performing at the charity gala, alongside Little Mix and JLS.
Little Mix also flashed the flesh, with all the girls choosing to wear a revealing crop top. Perrie Edwards, Jesy Nelson, Leigh-Anne Pinnock and Jade Thirlwall opted for a unified monochrome theme.
Fellow guests Eliza Doolittle and Ashley James also seemed to have got the memo about showing off plenty of skin... Singer Eliza wore a white two-piece, which exposed her tiny tum and plenty of leg, while former Made In Chelsea star Ashley showed off her perfect pins in a black dress with huge split up the side.
We're glad that even the plummeting November temperatures didn't stop the gorgeous ladies from showing off their best assets!
The sold-out dinner with cocktails took place at London's Roundhouse, and was hosted by Marvin Humes, Dave Berry and Lisa Snowdon.
What do you think of Jessie J's revealing outfit? Tell us below, as the best comment from across the website each week wins £50!
Watch the video for Jessie J's single 'Thunder':