The 29-year-old performed the track on the finale of American Idol last night and has since made it available on the US iTunes store.
'1+1' was co-written by Beyoncé along with previous collaborators The-Dream, Christopher Stewart - who both worked with her on 'Single Ladies' - and Corey Jackson Carter.
The track is a slow R&B power-ballad and serves as the opener for the singer's upcoming album 4.
'1+1' has not yet been given a release date outside the US.
> Beyoncé unveils '4' album tracklisting
Watch Beyoncé perform '1+1' on American Idol below: