The circuit takes its name from Clady Corner, a junction on the B39 road between Antrim and Belfast. In Irish, Clady derives from Clóidigh, meaning "washing river." The course was first used in 1922 for the Ulster Grand Prix and measured 20.500 miles (32.992 km) in length. The original route began near Loanends Primary School on the B39 Antrim to Belfast Road and wound through a series of public roads including the Seven Mile Straight between Antrim and Clady Corner, the A52 Belfast to Crumlin Road between Clady Corner and Thorn Cottage, a tertiary road running north through RAF Aldergrove towards Greenmount, and a return leg from Greenmount to Muckamore Corner at the B39 junction.
Racing on the full circuit continued until 1939, covering seventeen years of Ulster Grand Prix history on a course demanding sustained high-speed commitment across the flat agricultural landscape of County Antrim.
After the Second World War interrupted racing for several years, the Clady Circuit returned in 1947 in a revised form. The new layout measured 16.467 miles (26.501 km), achieved by cutting out the Aldergrove section that had previously run from Thorn Cottage through RAF Aldergrove to Greenmount. The shortened course ran from Clady Corner to Nutts Corner on the A52 Belfast to Crumlin Road, then used a section of the A26 Banbridge to Coleraine Road from Nutts Corner to Muckamore House near Antrim before returning to the start.
This post-war configuration hosted the Ulster Grand Prix as part of the FIM Motorcycle Grand Prix World Championship until 1952, when the circuit was abandoned for motorcycle racing. From the 1953 season onward, the Ulster Grand Prix moved permanently to the Dundrod Circuit, also in County Antrim, which remains its home to the present day.
The Clady Circuit produced outstanding speeds for the machinery of the era. On the original long circuit, the outright lap record was set by Dorino Serafini during the 1939 Ulster Grand Prix, riding a 500cc Gilera motorcycle to a time of 12 minutes and 17.8 seconds at an average speed of 100.03 mph (160.98 km/h).
On the shortened post-war layout, Les Graham set the lap record during the 1952 Ulster Grand Prix, lapping in 9 minutes and 21 seconds at an average speed of 105.94 mph (170.49 km/h) aboard a 500cc MV Agusta 4C. That 1952 race also produced the circuit's race record: Cromie McCandless averaged 99.79 mph (160.60 km/h) on a 500cc Gilera across the full race distance, narrowly missing triple figures on the race-average measure while demonstrating the circuit's extraordinary pace.
The Clady Circuit's two decades of competitive use placed it among the premier motorcycle racing venues in the British Isles. Its long, fast straights through the Antrim countryside provided a template for the high-speed road racing culture that the Ulster Grand Prix has maintained ever since, even after the move to Dundrod. The Seven Mile Straight section in particular became synonymous with outright top-speed heroics in the pre-war era. Though the roads that formed the Clady layout returned to public use after 1952, the circuit's contribution to the development of the Ulster Grand Prix and Irish road racing more broadly is acknowledged as foundational to the sport's Northern Irish heritage.