Louis, in a black Mercedes, was the first to arrive, followed by sharply-suited head judge Gary.
The pair stopped and chatted to fans before Tulisa stole the limelight in a gorgeous teal dress.
The N-Dubz singer took the opportunity to drum up support for her act, shouting "Vote Little Mix" as she made her way towards the entrance to Wembley Arena.
She shivered as she took the time to greet fans, even stopping to look at a photo of herself on one teenager's mobile.
After a lengthy wait, diva Kelly was the last to arrive, decked out in sky-high stilletos and a short black dress.
But she made it up to the crowds by chatting and posing for pics, even running back for another photo as security staff tried to drag her inside.
Charlotte Buckland, 16, who travelled all the way from Newcastle without a ticket in the hope of seeing her favourite act Little Mix, said the red carpet experience was well worth the journey.
The thrilled teen gushed: "It was amazing!
"Tulisa looked so stunning and spent loads of time talking to fans.
"I was hoping Little Mix were going to come out for a photo but even without that, this has made my year."
The crowds were unable to get a glimpse of their favourite acts, who were already preparing inside the arena.
Tonight's show will see Little Mix, Marcus Collins, and Amelia Lily duet with the judges in a last bid to take the X Factor crown.
Kelly and Amelia will sing Ike and Tina Turner's River Deep, Mountain High, while Tulisa and Little Mix will perform a medley of Alicia Keys hits.
Marcus and Gary are performing Billy Joel's She's Always a Woman.