The work is scheduled to be finished by the end of July, when visitors can expect to see a new entrance hall and reception area, and there will be a fresh look for the outside of the building, too.
Several rooms will be brought back into use, and more changing spaces will be created. While the works are under way, bookings are still being accepted, and a new website will be launched to promote the baths.
Harrogate Borough Council’s cabinet member for culture, tourism and sport, Stanley Lumley, said: “We compete in a competitive market and it’s essential we make sure the facilities we offer, and the experience a visitor receives, is as good as it can be.
“This refurbishment will transform more of the public areas of the building and bring back into use several rooms which have been hidden away for many years.
“I’d like to thank our regular customers for their patience while the work is carried out. I can assure them the wait will be worth it.
The upgrades are part of Harrogate Borough Council's five year development strategy for the Turkish Baths.
At a cabinet meeting in August last year, councillors supported a report which set out plans to create new facilities, including a wet spa and thermal space, more treatment rooms, and beauty services.
Coun Lumley said a line of Turkish Baths products will be introduced to develop the attraction’s brand.