The Yarmouth lifeboat transferred the passenger to a waiting ambulance after a medical emergency was declared as the freight and passenger ferry left the south coast of England.
The current condition of the unidentified casualty is not known.
In a statement, a Condor spokesman said: ‘We can confirm there was a medical emergency on Commodore Clipper while en route to the Islands from Portsmouth.
‘The passenger with a pre-existing medical condition was attended to by our team on board. Their condition was assessed and medical advice recommended further treatment ashore.
‘The Yarmouth lifeboat was therefore called to meet the ship approximately 12 miles south-west of the Isle of Wight and the casualty transferred.’
The spokesman added: ‘Decisions are always taken in passengers’ best interests and on this occasion, a ship to ship transfer was deemed the most appropriate course of action.
‘We do appreciate the empathy shown by other passengers as we dealt with the casualty. Condor crews across its fleet are trained to handle a range of medical emergencies.’