The singer celebrated at 55 Club London last night (Oct 4) and made sure she looked amazing.
Wearing a black fitted dress, with gold embellishment around her cleavage and a thigh-high split, Leigh-Anne looked elegant and chic.
She teamed the look with big hair, gold hoop earrings and towering peep-toe heels - Christian Louboutin naturally!
Jade Thirlwall, Jesy Nelson and Perrie Edwards also looked stunning - Jesy in a leather two-piece, Perrie in a long clingy black dress and (our personal fave) Jade's electric blue all-in-one.
Perrie shared the love on Twitter, writing: "Happy birthday Leigh Leigh (Pocahontas) my beautiful sister! I love you more than anything! Hope you have the best birthday ever! Perrie."
Jade wrote: "Happy birthday to one of the most beautiful,kind,talented girls I know! So proud to be part of ur life, love you long time Pocahontas xjadex."
While Leigh responded: "Thank you so much mixers and my beautiful girls for the bday messages I love u all so much! Now time to party! X :D @55ClubLondon leigh x."
Earlier this week, Little Mix announced their second album will be called Salute and is available for pre-order from Monday.
Do you like Little Mix's look? Tell us what you think in the comment box below!
Watch the video for Little Mix's single 'How Ya Doin'? ft. Missy Elliott':