Capita will provide customer services, policy administration, new business, claims activities and the associated technology for around 4.5 million policies across CIS's life, pensions and unit-trust operations.
Capita will also be providing a platform to enhance CIS's new product development.
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.