The ship, called Normandie Express, is currently undergoing engineering checks and sea trials and is due to be renamed Condor Voyager.
Once the vessel has been fully evaluated and approved for use, it is expected that it will visit Guernsey and Jersey to conduct harbour berthing trials next month. Familiarisation training will be held for staff.
At 98 metres it is ten metres longer than Condor's similar Rapide vessel and can carry 850 passengers and 250 cars.
In March last year, investment company, Columbia Threadneedle and Brittany Ferries – a minority stakeholder – bought Condor.
Elwyn Dop, Condor's operations director, said the ship-sharing agreement was a 'great example' of the two ferry businesses working together.
'The ship is proven cross-Channel and is a larger version of Condor Rapide, so we feel she is suited to providing services to the islands and will offer a greater car and passenger capacity. These sea and berthing trials are also important for Brittany Ferries’ and our own teams working together,' he said.
He added: 'Part of the agreement is for Condor to provide a number of peak summer services for Brittany Ferries between the UK and France.
'We are excited that our new owners share the same vision for developing ferry services and taking on this ship is one example of how our partnership and sharing of expertise can benefit the Islands.'
The vessel, which has been part of Brittany Ferries' fleet since 2005, can travel at 42 knots [48.3mph] and normally operates summer crossings between Portsmouth and France. It was built by Incat – the Australian company which built Condor's Rapide and former Express and Vitesse ships.