The supplier will provide customer services, policy administration, new business and claims activities, and the associated technology for some 4.5 million policies across CIS's life and pensions and unit trust operations.
Capita will also be providing a platform to enhance product development at the insurance firm, which is part of Co-operative Financial Services.
Capita and CIS first announced the proposed deal last November, with a then estimated value of £250m. Now that the deal has been signed, more than 800 CIS staff will transfer to Capita under Tupe terms on 19 November.
The work will continue to be delivered from a central Manchester base.