Tokyo Gas joins EDP Group, Repsol, Aker Solutions, and ASM Industries as backers of the US-based firm.
The additional funding will help push Principle Power's WindFloat semi-submersible floating platform towards commercialisation, the company said.
Principle Power has been operating in Japan for a number of years. In 2017, it signed a collaboration agreement with Mitsui Engineering & Shipbuilding (MES) to promote WindFloat projects in the region.
It also has other projects off Portugal, the UK and the US.
"The investment by Tokyo Gas sets a strong foundation for our expansion in Asia, which is expected to lead global floating offshore wind development in the coming years," said Principle Power CEO João Metelo.
"Closing this deal in the current business environment overshadowed by the Covid-19 pandemic, while a significant achievement on its own, demonstrates the very solid fundamentals of our industry in building a resilient clean energy economy," he added.
At the company's WindFloat Atlantic site, the final turbine has set sail from the Port of Ferrol and is making it's way to the project site 20km off the coast of Portugal. The 25MW site comprises three MHI Vestas V164 8.4MW turbines.