The charity says the bird would have been subjected to "unimaginable" suffering if the video footage is accurate.
-> Police inquiry into assault on 13-year-old boyIn the footage, which was passed to the RSPCA, the man - wearing a yellow hi-vis jacket - appears to hit the bird from its nesting place with a stick.
He grabs the flapping bird from the floor before apparently biting the head from its body.
The man appears to spit the head out of his mouth then throws the decapitated pigeon, whose wings are still moving, to the ground.
He picks the bird up to pose with it for the camera, then walks away.
-> Investigations continue into deadly helicopter crash in YorkshireLaughter can be heard from other people at the scene, believed to be a building site with possible links to the North of England or Wales.
Dermot Murphy, assistant director of the RSPCA inspectorate, said: "This is a deeply shocking, disturbing and distressing video, appearing to show a man biting the head off a live pigeon.
"If what this video seems to show is accurate, the pain and suffering caused to the pigeon is likely to have been unimaginable.
"Biting the head off a pigeon is likely to constitute an offence under the Animal Welfare Act 2006.
-> 'Truly sorry' Northern Rail warns it will take weeks to improve services"We're very eager for information identifying the individual involved, or providing related background, to be brought to our attention as a matter of urgency.
"It has been suggested to us that the incident may have links to either the North of England, or Wales.
"However, we are eager for any information which could assist with our inquiries on this serious matter."
Anyone with information is asked to call the RSPCA's inspectorate appeal line on 0300 123 8018.