The 'Wherever You Are' collective, made up of the partners of military servicemen, approached the reality star and serving soldier to appear on their new release.
"What the Wives have achieved in giving support to military families is incredible," Kerr told The Sun. "To be part of their journey is very special for me."
Kerr, who was eliminated in the first week of last year's live X Factor shows, is a private in the 3rd Battalion, The Yorkshire Regiment.
The 27-year-old is scheduled to return to Afghanistan on February 26 for a six-month tour of duty.
Addressing Kerr's appearance on the song and his forthcoming deployment, Military Wives mentor Gareth Malone tweeted to him: "Congratulations! Honoured to have you singing on the track. Be safe."
The Military Wives famously won the 2011 Christmas No.1 battle against Kerr's X Factor co-stars Little Mix.
They will release their debut album, also called In My Dreams, on March 5.
Listen to 'In My Dreams' by the Military Wives and Jonjo Kerr below: