The songwriting duo - who together have penned pop hits such as 'Angels', 'Let Me Entertain You' and 'No Regrets' - have penned an original track for the project after being approached by producers via music supervisor Liz Gallacher.
The movie will also star Catastrophe's Sharon Horgan and will be directed by 'The Full Monty' filmmaker Peter Cattaneo and it is inspired by the BBC documentary series 'The Choir: Military Wives'.
The plot will focus on a group of women who form a close bond and eventually a choir to help them cope with the stresses of being separated from their loved ones who are serving in the armed forces.
It is not yet known if Robbie, 44, will also sing the track he is writing with Guy, 56, for the soundtrack or whether it will recorded as choir song in keeping with the movie's story.
The score will be provided by 'Mission: Impossible - Fallout' composer Lorne Balfe.
Speaking about the movie song, Robbie and Guy released a joint statement which read: ''It's always a joy to work together on new music, and we're thrilled that our new song will be featured in this special film. We're really proud of the track and can't wait for you
all to hear it.''
A statement from the production team added: ''Over the last few months, Kristin, Sharon and our hugely talented ensemble cast have put their hearts and voices into telling this tale, which demonstrates how a community of strong women can come together and literally change lives. Having Robbie and Guy collaborate with us on the original music, which is so essential to the journey of these characters, is truly exciting.''
'Military Wives' will also star 'Downton Abbey' actress Emma Lowndes, Greg Wise, Jason Flemyng, Gaby French, Lara Rossi (Robin Hood), Amy James-Kelly and India Ria Amarteifio.
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