And its new owner, the Paramount Hotel Group, says it will spend £2 million turning the three-star seafront hotel into a four-star establishment over the next 18 months.
All 152 bedrooms will undergo a refit, followed by alterations to the reception area. Paramount also has plans for better exterior lighting.
Marketing manager Caroline Sims said: "The Old Ship used to be a four-star hotel but due to a lack of investment it has become three-star.
"We hope to get the old status back within a year. Bedrooms need to be improved to give the place better standards."
The heritage-listed Old Ship will remain open during the work, with corridors closed off one at a time.
Ms Sims added: "The Old Ship has a great reputation. Visitors and local people hold it in a great deal of affection. We will not be altering the facade, except to improve the lighting.
"At the moment people driving past at night might not even notice it but, hopefully that will change."
Paramount owns eight other hotels around the country.
Managing director Michael Purtill said: "This property has a fantastic heritage and is known for its high level of service.
"We want to enhance the reputation through investing in facilities for guests."
The Old Ship was, for many years, Brighton's best known hotel and featured in the novel Vanity Fair, by William Thakeray.
It served as an inn as early as 1559 and historians believe its name comes from being partly built from ship's timbers.
The modern frontage dates from last century.
Mr Purtill added: "This acquisition is part of our plans to develop the Paramount Group across the country.
"We are keen to maintain the identity and history of the Old Ship."
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