The builder was in the bucket of the hydraulic lift when it was hit by a number 45 bus in the Euston Road opposite St Pancras station.
He was knocked out of the cherry picker and fell to the street where he was then hit by the same bus and dragged 20 metres along the road.
Paramedics took him to hospital with serious head injuries. His condition was first described as critical but was later said to be serious but stable.
The London Evening Standard said the workman is understood to have been working on the refurbishment of the five star St Pancras Renaissance hotel.
Galliford Try is main contractor on the £103 contract to transform St Pancras Chambers into luxury apartments and a hotel and the job is now at the finishing stage.
Two lanes of the eastbound carriageway of the Euston Road were closed for several hours after the accident at 5.10am causing long delays for commuters.
Officials from the Health and Safety Executive were called in to investigate the incident.
The top window of the bus was shattered in the collision but no-one on the bus was hurt.
The cherry picker is believed to have been in the forecourt of the hotel and the workman was in the lift’s arm which was being extended when it was hit.