The singer also released a music video to accompany the song on her official YouTube page last night (October 1).
The track heads up the star's as-yet-untitled third studio album, which follows next year.
The record follows up 2008's Sol-Angel and the Hadley St. Dreams, which peaked at number nine on the US Billboard chart and spawned the hit singles 'I Decided' and 'Sandcastle Disco'.
The 26-year-old mother recently admitted that she wouldn't be giving her older sister Beyoncé parenting advice, adding: "I think it's actually the most annoying thing when you're a new mum and you're getting so much advice from other mothers!
"You really just have to feel it out for yourself. But she's my best friend and we talk at least every other day."
Watch the music video for 'Losing You' below: