The BT Pension Scheme is selling its majority stake in Hermes.
The deal worth £246m will see New York-based fund giant Federated Investors take control of the asset manager.
BT Pension Scheme will retain a 30 per cent stake in Hermes, continuing to invest as a client.
Hermes’s management will retain an interest of around 10 per cent.
The transaction values Hermes at £410m.
Hermes has been managing The BT Pension Scheme since 1983 and is responsible for £33bn of assets under management.
No jobs are reported to be at risk.
Federated is one of the largest US fund houses and has a total of $397.6bn (£278.5bn) in assets.
The deal follows a growing trend of mergers in the asset management industry, the most notable being the acquisition of Aberdeen Asset Management by Standard Life earlier this year.
BT Pension Scheme trustee chair Paul Spencer says: “Hermes has delivered excellent investment performance and stewardship to the scheme over many years, operating initially as our in-house manager and in recent years, building on this capability to develop a strong multi-client business. This transaction is the next step in the evolution of Hermes, as it continues to expand its global business.”