The acts have teamed up to record 'Learn Me Right' for the soundtrack to Disney Pixar's new film Brave.
Speaking about 'Learn Me Right', Marcus Mumford previously told NME: "It's quite fun doing a song for a movie rather than for an album.
"We liked the idea of having an orchestra in the background and having a girl like Birdy sing - it's been quite liberating."
Birdy added: "I love it because it tells a story. Although it has a lot of emotion, it's also very upbeat and you want to dance to it, which is why it works so well."
It is the first new song from Mumford & Sons since their 2009 debut album Sigh No More, which has sold over 3 million copies in the UK and US alone.
Brave will be available in cinemas from June 22 in the US and August 17 in the UK.
Listen to Mumford & Sons and Birdy's 'Learn Me Right' below: