The 46-bedroom hotel which was originally built in 1438, had to put the Orangery through a number of planning processes, including having to be approved by Historic England, before it could be given the green light for construction.
When completed early next year, the Orangery will be used for weddings, conferences and events for up to 300 people and allow the venue to hold trade exhibitions for the first time.
Tom Gilbert, head of sales and marketing at Rushton Hall, said: "This is a very exciting time for us here at Rushton Hall. Being such a popular venue for events, we wanted to not only offer our guests something extraordinary but also cater for a larger number of guests in spectacular surroundings.
"The Orangery will be a stunning wedding venue and its flexible layout makes it ideal for conferences and events too. We will also now be able to hold trade shows and exhibitions, something that we have not been able to do previously. Six bedrooms with access to the wonderful gardens will also be added”.
The Grade I Rushton Hall, set within 25 acres of land on the borders of Northamptonshire and Leicestershire, was completed in 1600 with the creation of a front gallery by Thomas Tresham.
Construction work for the Orangery, which started last week, will take place in five stages with the same stone to be used as the rest of the hall.