Embodiments described generally relate to methods for assembling a modular floating production storage and offloading (FPSO) vessel. A cargo module section, a forward module, and a rear module can be positioned and aligned with each other such that the cargo module section can be disposed between the forward module and the rear module. A plurality of connectors can be coupled together to secure the forward module and the cargo module section together and another plurality of connectors can be coupled together to secure the rear module and the cargo module section together. A first topside module can be installed onto or over an upper surface of the forward module and can include a flare tower, a turret, hydrocarbon production equipment, or any combination thereof.