The work is expected to take 12 weeks as workers dump thousands of tonnes of Norwegian boulders at the end of the pier to shore it up.
Assistant Economic Development Minister Alan Maclean, who has responsibility for Harbours and the Airport, said that the work would protect the breakwater below the surface of the water.
He said it could add a century to the life of the pier – the longest pier in Jersey – which has been in place for 150 years.
A barge sitting off St Catherine is holding 10,000 tonnes of boulders, each weighing up to 35 tonnes, and three more similar loads are expected.
Deputy Maclean said that after looking around Europe for a source of enough rock to carry out the work, they had settled on Norway because even including shipping costs, it had proved the cheapest option.
But some boulders dislodged from the existing face at the end of the breakwater are being replaced by boulders from La Saline quarry, added Deputy Maclean.