The 209-room Studley Castle hotel in Warwickshire is to reopen in March 2019 following a £50m injection of cash from Warner Leisure Hotels.
The refurbishment of the 19th-century, Grade II*-listed property will mark the largest investment every undertaken by Warner, which owns 14 hotels in the UK.
Around £26m is being spent on restoring the castle and reinstating original features. The remaining £24m is being invested into modernising aspects of the building, including a new live music venue.
Simon Thompson, managing director of Warner Leisure Hotels, said: "Studley Castle signals a significant investment in the start of an exciting new era for Warner. We have a unique proposition in the market and Studley is set to support our growth in helping us become more relevant to existing and new audiences."
Originally the home of the Lyttleton family, Studley Castle has also been occupied by a horticultural training college and a marketing centre for Rover.