The X Factor star thanked fans for downloading the track after it knocked Ne-Yo's 'Let Me Love You (Until You Learn To Love Yourself)' off the top spot.
"Cannot thank every single one of you guys enough for everything, can't believe I'm number 1 on iTunes, let's make sure it stays there Lilys!" she tweeted.
Meanwhile, X Factor judge Tulisa Contostavlos currently sits at number 13 on the iTunes chart with her new single 'Live It Up', which features US rapper Tyga.
Speaking of her upcoming debut album, Lily recently told Digital Spy: "There's a ballad on there which I absolutely adore and it really shows the soul side to my voice.
"People think of me as a rock chick but people forget my first audition when I sung 'Piece Of My Heart'. There's a bit of dubstep on there as well which I think will surprise people!"
Watch Amelia Lily's video for 'You Bring Me Joy' below: