The Ørsted East Coast Hub will be the largest port facility of its type in the UK and used to serve the firm's UK North Sea projects.
The site is located in the Royal Docks in Grimsby, northeast England. It will extend Ørsted's current facilities on the site built in 2014 to provide a base for the 270MW Lincs and 210MW Westermost Rough offshore wind projects.
Up to 200 jobs could be created by the port expansion, on top of the 150 currently on-site, Ørsted said.
Ørsted has hired construction firm Hobson & Porter, which built the initial O&M base four years ago, to carry out the new round of work.
The hub will host service vessels capable of accommodating up to 60 crew and technicians. It will also include a comprehensive marine and helicopter coordination centre to provide continuous service to offshore operations in Europe, the developer said.
Matthew Wright, Ørsted UK managing director, said: "Offshore wind is a major economic engine for the Humber region, and this multi-million-pound investment demonstrates our long-term commitment to the area."
Ørsted is developing two of the biggest wind farms in the world off the Yorkshire Coast, Hornsea Projects One and Two with a combined 2.59GW of capacity.
The Danish firm is currently involved in operating 1.85GW of offshore wind capacity off the UK's east coast.
"This state-of-the-art facility will be the base for the hundreds of workers both constructing these projects, and operating and maintaining the projects we already have in the area," Wright added.