January 1964 saw the debut of the classic Marcos, in the shape of the Marcos 1800 GT at the London Racing Car Show. The reception was incredible and it "stole the show".

This new Marcos was way ahead of its time with an ultra fastback shape and rakish profile.

The 1800 consisted of an all wooden chassis with an enveloping fibreglass body. The body, being bonded to the chassis, formed an immensely strong but extremely light construction. The chassis strength was obtained by transferring all of the loads through the central spine and the two unique triangular torsion boxes which ran the length of the sills. The chassis was constructed largely from 3mm Gaboon ply, with Sitka Spruce lippings and Douglas Fir ply. Areas including the floor and boot used balsa and insulation board for lightness. The whole structure was bonded and stapled together using Aerolite 306.

The car’s design featured twin headlamps under perspex covers, a steeply sloped bonded windscreen, and a high nose for aerodynamic purposes. Early cars can be distinguished by the "elephant ears" on the scuttle. These were a very crude form of air intake mounted directly in front of the windscreen which acted as a shower in wet weather and were soon discarded. Later changes included scalloped wheel arches, a flip-up boot lid and louvres on the bonnet. The 1800 was one of the lowest cars ever produced at less than 41.5 inches. The Ford GT 40 being 40in.

The 1800 had been launched as a road car, but soon became very popular with club racers etc. With amazing performance and a racing-car like seating position, the 1800 was a winner from the beginning.   
The 1800 cockpit was extremely well appointed for its day. The semi reclining seats and high, almost overwhelming transmission tunnel held the occupants more than adequately even under racing conditions. The futuristic dashboard consisted of a centre section enclosing minor instruments and switches. Either side the dash was scalloped to house the rev counter and speedometer for the driver, and a generous glovebox for the passenger. In view of the cost of manufacture this style of dashboard was dropped on future models.

One of the unique features of the 1800 was the adjustable pedal assembly, the hall mark of the Marcos, the whole pedal assembly moved backwards and forwards as opposed to the seat, a feature used on all Marcos cars until the year 2000. The 1800 was also one of the first ever cars to have head restraints fitted as standard equipment.

Other features of the 1800 included the Marcos Electron wheel, manufactured in ultra lightweight cast magnesium. 

Early cars were fitted with Independent Rear Suspension - Marcos's unique system with a De-Dion tube, cast alloy leading link and telescopic spring damper units which incorporated inboard drum brakes on the early cars and inboard discs on later cars. A live Axle was soon introduced with three radius rods, and a Panhard rod, this was quickly changed to four radius rods to transmit the loads into the chassis more effectively. The early cars used the Volvo B18 engine, and the last cars the B20 engine. Both B18 and B20 engines were used in race cars, with the option of overdrive.

The 1800 was displayed at the 1965 Racing Car Show and was described as "probably the most elegant car in the show".

Sales started to flag in 1966, and the decision was made to streamline production and reduce the cost of manufacture. The 1800 was discontinued with the arrival of Ford's 1500 GT engine. Of the 100 cars built at Greenland Mills in Bradford on Avon, 52 cars were IRS and 38 were Live Axle cars.