The indie-pop collective - fronted by Florence Welch - have been working on a follow-up album to 2009's Lungs over the past year.
The new song, titled 'What The Water Gave Me', was performed during their show at the Greek Theatre on June 12.
It is not yet known whether the track will make the new album's final cut as the decision on the confirmed tracklisting is to be made at the end of July.
Welch recently revealed that the new album will contain songs about "imaginary things", such as "ghosts and rumours".
Watch a fan-recorded video of Florence and the Machine performing 'What The Water Gave Me' live below: