Aegon has struck a deal with Atos to service and administer its existing off-platform business for the next 15 years.
The deal will affect about 1.4 million customers with a number of different types of policy, including pensions and endowment policies.
It will see Aegon staff move over to Atos, and the provider has promised clients will not see any changes to the service they receive.
Aegon already has a relationship with Atos, which has serviced and administered Aegon’s 500,000 protection customers since 2016.
Under the agreement Aegon will continue to be the product provider and carry out the regulatory responsibility for the products, many of which stretch back 40 years.
Adrian Grace, chief executive of Aegon UK, said: "It’s important that as the financial services market evolves we continue to provide customers with an excellent service, stability and help them achieve a lifetime of financial security.
"Building on our established and already successful relationship with Atos will give continued momentum to our existing business.
"This is an important step in our strategy and is in the best interests of our customers, employees and shareholders."
Aegon stressed the move would not affect on-platform clients and was unrelated to its recent well-documented replatforming struggle, which was managed by its digital solutions business.
The agreement is expected to save Aegon about £10m a year in running costs initially, growing to £30m over time.
Total transition and conversion charges are estimated to amount to £130m over the first three years of the agreement.
Adrian Gregory, chief executive of Atos UK & Ireland, said: "We look forward to working with the Aegon team to deliver operational and end-to-end customer service excellence, by blending the existing talent with tailored innovative technologies.
"This agreement also highlights the increasing footprint and ambition of Atos in providing business transformation expertise to the life and pensions market and the broader financial services sector."
Staff will remain based in Edinburgh, where Atos plans to build a centre of excellence in administration of life and pensions business.
Brian Linn, general secretary of workers trade union Aegis, said: "We are encouraged that Aegon’s review of existing business has resulted in a solution that guarantees the future of the Edinburgh site and provides opportunities for growth with a commitment to no offshoring of jobs.
"Our first impression is this is very positive news for our members regarding their job security and career development. We look forward to working with Aegon and Atos to ensure that our members’ interests are promoted and protected during this consultation period and beyond."