The all-girl band is made up of Scarlett, Este Haim (from the band Haim) and singer-songwriters Holly Miranda, Kendra Morris and Julia Haltigan, and their first song is called 'Candy'.
New mum Scarlett describes the group's sound as "ultra-pop".
"The idea was to write super-pop dance music written and performed by girls," the 30-year-old actress told Rolling Stone.
"I wanted it to be like those bands: ultra-pop but also a little ironic, a little in on the joke."
On first listen, we're loving the catchy track's fun '80s-style sound and infectiously catchy beat - listen for yourself here.
This isn't Scarlett's first time flexing her vocal talents, of course! She has previously released an album of Tom Waits covers in 2006, and in 2009 she partnered up with singer/songwriter Pete Yorn for an album called 'Break Up'.