The English indie group posted 'Angels', also the first track on their new record, on YouTube.
"It's been a long time since we've played you anything new. This song is called 'Angels', it is the first single from our new album, Coexist," the band said in a statement.
"We've been playing this song live recently, so it feels good to share with you the version we've been working on for so long. We hope you like it."
'Angels' will be available to download from midnight tonight through iTunes and Spotify.
The xx have also unveiled the tracklisting and artwork for Coexist - the group's follow-up to their Mercury Prize-winning debut album xx in 2010 - to be released on September 10.
The Coexist tracklisting appears below:
10. Swept Away
11. Our Song
They began work on Coexist back in November 2011 with member Jamie xx, aka Jamie Smith, in charge of production duties for the project.
The band have since revealed that all songs from their second LP will be love songs.
The xx are currently on a world tour playing various festivals across the globe and will next perform in the UK at Bestival on September 7.