The three-minute upbeat pop tune marks the musical return of Geri Horner, Emma Bunton and Mel B, who have come together again without bandmates Victoria Beckham and Mel C, who have refused to participate in the comeback.
'Song For Her' is a chorus-heavy track about female empowerment, with the girls repeatedly singing in harmony: "This is a song for her/ You know you light it up/ You know who you are/ Stand up, stand up/ She's got that boom-boom pop/ That's something they can't stop/ She's got that song for her."
Emma, 40, insisted earlier this year that 'Song For Her' - which has appeared on Facebook and YouTube - was "not a single" and was instead the result of the girls just having fun in the studio.
She said in July of the then-unheard track: "You know, us girls love creating stuff. We went and had a laugh in the studio. It's not a single, it's just we were creating."
The girls were originally tipped to reunite this year, which would have marked the release of their breakthrough hit 'Wannabe', but Mel B admitted they are still finalising the details of their comeback.
She previously shared: "We are going to do something, us three. We're going to perform and celebrate together for the people.
"I think because we're a British band, we're probably going to start in London and work our way round."
The girls returned to the recording studio in November, but the specifics of their plans are still to be confirmed.
It has, however, been revealed that Victoria and Mel C will not participate in the project.