The musicians hope the song, called Peace For One Day, will be played by radio stations across the planet.
The pair has collaborated with British film-maker Jeremy Gilley who wants 21 September to become a global day of ceasefire.
Stewart said: "The idea was to make a song that on 21 September we'll get as many stations around the world to play, and DJs to talk about what it's all about.
"Simultaneously in all these countries there'll be millions of people listening."
Happy
The musician, who was in New York on 11 September last year, said he wanted the track to be "upbeat rather than a maudlin song".
He said: "We're not really making a single that we're trying to get in the charts. It's an idea to uplift people."
Jamaican star Cliff said he was happy to contribute and "play my part in this thing and what I do best is through music".
Film-maker Gilley has spent the past three years trying to motivate opinion-formers and world leaders into recognising the ceasefire day and the UN has passed a resolution acknowledging it.
He said he hoped that in 10 years' time every person in the world would have heard the song.
A number of events across 44 countries will take place to mark the date, including a concert at London's Brixton Academy headlined by acts such as Faithless, Zero 7 and Starsailor.
Action
Musicians such as Blur star Damon Albarn, Moby and the Sugababes have recorded messages of support for the night.
The proposed ceasefire day comes as the US looks for support from other countries to take action against Iraq.
Gilley said: "I think the timing is very profound and shows why every single head of state in the world voted for the first non-violence day."