Kelly Rowland's last remaining act finished in third place, leaving Little Mix and Marcus Collins to battle it out for the title in tomorrow night's episode.
Lily performed Christina Aguilera's 'Ain't No Other Man' and a duet of 'River Deep, Mountain High' with Rowland in tonight's Wembley Arena spectacular.
Speaking after the result, Lily told host Dermot O'Leary: "My ambition was to get to the final and I did it. This isn't the last of Amelia Lily."
The singer also thanked viewers who voted her back into the competition four weeks ago following Rowland's decision to eliminate her in the first live show.
The Destiny's Child judge proceeded to predict that Lily would have an "incredibly bright" future, adding: "She's the best vocalist here. I'm so proud of her and she's a star, an absolute star."
The X Factor final continues tomorrow (December 11) at 7.30pm on ITV1.