The London Assurance (LA) was incorporated in 1720, marking a significant innovation in the marine insurance industry. Contemporaries anticipated joint-stock firms such as the LA would rapidly outcompete private underwriters, yet this outcome did not occur. The success of the private underwriters has been ascribed to their organizational form. This paper reassesses these explanations and finds that, rather than an a priori worse business model, various corporate governance challenges limited the LA’s capacity to compete. This provides a more complete explanation for the relative failure of the joint-stock marine insurance companies and has implications for understanding the evolution of the corporate form in the eighteenth century.