The agency picked up the business after a pitch against Tribal DDB and R/GA.
LBi will now be briefed with developing FT.com's customer communications strategy, which will have a focus on media planning and buying, and customer relationship marketing. This will be supported by relevant brand creative, which will continue to be handled by Tribal DDB.
Frances Brindle, the global marketing director at FT.com, said: "LBi's expertise as a full-service agency meant its skills and understanding in customer communications planning and media stood out from the rest. It offers the full package."
Judith Carr, the client partner at LBi, added: "We are thrilled to be working with FT.com. It is both reassuring and a testament to the work and skills of our team to see that the benefits of a full- service agency are being recognised and used by such a well-respected brand."
Launched in 2005, FT.com has 5.3 million unique monthly users.