The chief executive officer of a San Francisco investment bank prevailed in a hard-fought election to join the board of Finra, the front-line regulator of stockbrokers, knocking off an incumbent and a well-known challenger who campaigned on the message that rigid oversight is choking small firms.

Bob Muh, the CEO of Sutter Securities and a former Bear Stearns partner, narrowly defeated three other candidates to win a seat on the board of the Financial Industry Regulatory Authority.