Tequila\London, the incumbent on the business, discovered it had lost the account last Friday. Draft FCB and Claydon Heeley were eliminated in an earlier round.
Rapier has been briefed to develop all the healthcare business' direct response communications over the next five years as it seeks to achieve market leadership.
The company has increased its budget by £10 million a year in an attempt to dislodge the three major players - Bupa, AXA PPP and Norwich Union - that dominate the private medical insurance market.
Mark Savage, PruHealth's head of direct sales and marketing, said: "Rapier has a proven mix of skills and experience to help us achieve market leadership."