More than 40 personnel from across the emergency services were called to help with the incident, after a 999 call was made shortly before 10pm.
Several police officers climbed down the cliff to the casualty and provided first aid as soon as they could get to the teenager.
The St John Ambulance inshore rescue boat was called into action at 10.36pm after it was decided that the safest and quickest way to rescue the teenager would be from the water's edge.
The boy was on board the rescue boat in around 30 minutes.
He was picked up by an ambulance crew at St Peter Port harbour and quickly taken to Accident and Emergency.
