Utmost Group has agreed to acquire Quilter International, subject to regulatory and other approvals.
Quilter will receive approximately £483m in cash assuming completion on 31 December 2021.
Quilter International will become a part of Utmost International, the international life assurance business of Utmost Group.
The deal adds £22bn of assets under administration and 90,000 policies to Utmost International.
Utmost International will have £52bn of combined assets under administration, 220,000 policies and would have written over £330m APE of new business in 2020, making it "a leader in the industry".
Paul Thompson, CEO of Utmost Group, said: "This is a highly attractive acquisition for Utmost Group and underscores the importance of our Utmost International business. Quilter International is highly complementary to our existing International business from both an operational, product and distribution perspective.
"The acquisition is in line with our growth strategy and positions us well to benefit from the fundamental growth trends in the international life assurance sector.
"The acquisition confirms Utmost Group's position as a leading insurance consolidator with £58bn of assets under administration and 600K customers on a pro-forma basis and gives us an enhanced platform to pursue acquisitions.
"I look forward to welcoming all the staff, customers and distribution partners to our Group. We are delighted to work with Quilter on this transaction and look forward to a productive partnership in the future."
While Paul Feeney, CEO of Quilter said: "We are delighted to announce the proposed sale of Quilter International to the Utmost Group which represents an excellent outcome for all stakeholders.
This is a highly attractive acquisition for Utmost Group and underscores the importance of our Utmost International business."
"I would like to thank all our Quilter International colleagues for their dedication, professionalism and service to our customers, which has resulted in the creation of such a strong franchise.
"I am confident that the agreement we have reached with the Utmost Group will ensure the continued success of the business, with a focus on delivering good customer outcomes, as well as providing wider range of career opportunities for Quilter International's employees within an enlarged international business."