It is believed the dead man fell from the fifth floor of a scaffold and hit two colleagues on the way down.
One of the injured men was taken to hospital with chest and abdominal injuries, while a third man suffered minor injuries.
Health and Safety Executive inspectors are currently trying to determine the exact cause of the accident on Upper Richmond Road in south west London.
The site is a former office block which is being turned into luxury apartments by developer St James.
A spokesperson for St James’ owner Berkeley said: “This morning we were alerted to an incident at St James’ Langham Square Development.
“It is with great sadness that we learned that a sub-contractor had been fatally injured.
“We are investigating this incident as a matter of urgency. Our sympathies are with the family of the contractor at this time.”
A Metropolitan Police spokesman said: “At this early stage it is believed to have occurred after a man fell from a platform at the site and subsequently made contact with the other two men.”