Set up by former ITV comms chief Mark Gallagher last December, Pagefield won the brief from Jersey Finance via a three-way pitch.
The agency will promote the jurisdiction's financial services sector in the UK, handling corporate media relations and public affairs.
International offshore financial centres, such as the Cayman Islands, Bermuda and Luxembourg, have been criticised over their contribution to the global financial crisis because of a perceived lack of regulatory oversight.
Gallagher, senior partner and founder, said: 'We are looking forward to taking on the island's critics and explaining the enormous contribution that Jersey, and the other Crown Dependencies, make to the proper functioning of the UK financial markets and to the UK economy.'
The team will be led by Jersey-born partner & chief of staff Sara Price.
Meanwhile, the agency has also won a contract with the Institute of Chartered Accountants in England & Wales.
Pagefield's financial service offering sits alongside four existing practices: media sector, global institutions, a general practice and an overseas and foreign government practice.