Caffyns, in King Street, will be closing its doors on October 27.
The 70-year-old building was purpose-built to be a car dealership in 1936.
The distinctive art deco structure is ear-marked for future development as part of Mid Sussex District Council's plan to rejuvenate the town centre.
A source revealed the building is in need of a major refurbishment, "costing hundreds of thousands of pounds".
In a statement Caffyns said: "It is with great regret that Caffyns plc announces the imminent closure of its car dealership premises in King Street, East Grinstead.
"The company's presence in the town centre has lasted since the 1930s, housing various vehicle franchises in its distinctive round-towered building."
According to the spokesman, all members of staff were given notice a month before the closure and have been offered alternative positions within the company at other dealerships.
Simon Caffyn, chief executive of Caffyns Plc, said: "Naturally we are sad to be leaving East Grinstead after so many years."