The group recently shot the video for the single, taken from their upcoming fifth studio album.
Tom Fletcher announced the title on his Twitter page, writing: "I suppose its time to start revealing our secrets...you may or may not have heard but I can officially confirm that our first single back is...PARTY GIRL! (sic)"
The signer said that the track, which would be heard "soon", was written with producer Dallas Austin.
Dougie Poynter, who claimed that he wanted to call the track 'Barbie Girl', added: "Its about those chicks that go out dressed to kill then moan about guys hitting on them!"
The single is scheduled for release in early September.