Seymour Pierce director and head of investment banking Richard Feigen said the firm had appointed Capital following a three-way pitch but declined to comment further on the process.
He said Capital would be involved in drawing attention to the broker's work with larger capitalisation companies, such as Seymour Pierce's work on the flotation of its client Burren Energy.
Capital MD Steffan Williams is leading the account. Seymour Pierce has been without a retained corporate PR adviser since it split with financial comms shop Holborn following the buyout of the firm in 2003.
Among Seymour Pierce's more prominent staff are head of equities Richard Ratner and chairman Keith Harris.
Ratner is an authority on companies in the retail sector. Harris is a former chairman of the Football League and last year was reportedly in talks to buy shares in Manchester United to counter Malcolm Glazer's takeover bid.