River Road is based in Louisville, Kentucky and has around £2.2bn assets under management.
The transaction is expected to complete by the end of the first quarter.
Aviva says the deals supports its third party institutional asset management business by combining its existing expertise in fixed income in North America with River Road’s equity investment capability.
The management team and River Road’s investment process will remain unchanged. It will continue to be based in Louisville and will form part of Aviva Investors North America which is headquartered in Iowa.
Aviva Investors chief executive Alain Dromer says: “River Road will contribute significantly to our plans to increase our third-party institutional business and will help us provide our clients with a broader range of investment solutions.”