RELATED LINK: Listen to "This is It"
Jackson sounded confident and almost playful on "This is It," which features his trademark breathy vocal style, perfected over the years since he was a child sensation with the Jackson Five.
He is backed by lush vocals from his brothers, giving the recording a nostalgic, familiar feel.
It is a mid-tempo number with orchestral backing that is played during the closing sequences of the documentary, which opens Oct. 28 for a limited two-week run. It features rehearsal footage shot shortly before Jackson's death.
"This is it," goes one verse on the new song. "Here I stand. The light of the world. I feel grand."
The song is available on Jackson's official Web site and will also be sent to radio outlets.
It will also be part of the two-disc CD set that will accompany the movie in what is expected to be a worldwide marketing blitz to capitalize on the surge of emotion that followed the singer's death.
The documentary, also called "This is It," features footage of Jackson rehearsing for his planned London concerts, which were to mark his return to the stage after a lengthy absence caused in part by a series of legal and personal problems.
The singer was deeply in debt and had found his popularity dimmed by repeated charges of child molestation.
Jackson's death at age 50 is still being investigated.
The Los Angeles County coroner has ruled it was caused by acute intoxication by the anesthetic propofol, with other sedatives a contributing factor. The coroner found the powerful anesthetic was administered without any medical need and that recommended resuscitation equipment was missing.