This paper reports on the design of an open source-based control platform for the underwater remotely operated vehicle (ROV) Visor3. The vehicle’s original closed source-based control platform is first described. Due to the limitations of the previous infrastructure, modularity and flexibility are identified as the main guidelines for the proposed design. This new design includes hardware, firmware, software, and control architectures. Open-source hardware and software platforms are used for the development of the new system’s architecture, with support from the literature and the extensive experience acquired with the development of robotic exploration systems. This modular approach results in several frameworks that facilitate the functional expansion of the whole solution, the simplification of fault diagnosis and repair processes, and the reduction of development time, to mention a few.