About 10% of the land for the development is in Watford borough with the rest in the Three Rivers district.
Warner Bros said in its statement that “the expansion plan has been developed in close consultation” with the two councils “with careful consideration given to prioritising sustainability”.
The investment comes as Warner Bros Discovery’s productions in California have been hit hard by the first joint writers’ and actors’ strikes in more than six decades.
The walkouts have delayed major projects and prompted the company to cuts its revenue forecasts for the rest of the year.