By the mid-1980s Jaguar, under Tom Walkinshaw's racing organisation and designer Tony Southgate, had re-entered top-level endurance racing with ambitions to challenge Porsche and Mercedes-Benz in the ultra-competitive Group C category. The XJR-6 had established the basic template; sixty-four individual changes were incorporated to produce the XJR-8. Six cars were ultimately built — three new chassis plus three converted XJR-6s — all wearing the Silk Cut livery that became synonymous with Jaguar's endurance programme during this era.
The defining characteristic of the XJR-8 was its engine. Although outwardly similar to a production Jaguar V12, the unit was bored out to a full 7 litres, raising output to 720 horsepower (540 kW). This gave the car a distinctive high-pitched exhaust note, quite different from the deeper sound associated with the Porsche 956 and 962 opposition. Maximum speed was recorded at over 220 mph (350 km/h) on the Mulsanne Straight at Circuit de la Sarthe during Le Mans testing. The chassis followed the aerodynamic Group C formula with ground-effect tunnels generating high downforce for the high-speed circuits that defined the World Sports Prototype Championship calendar.
The XJR-8 entered the World Sports Prototype Championship at the start of the 1987 season and immediately demonstrated a competitive edge over the reigning Porsche 962. Victory came at Silverstone, the Nürburgring, and Spa-Francorchamps, and second place was secured at Fuji. Over the ten-round championship, Jaguar claimed eight victories in total, relegating Porsche and its vaunted 962 to second place in the constructors' standings. The team won both the drivers' title and the overall manufacturers' championship in dominant fashion.
Three XJR-8s were prepared specifically for the 24 Hours of Le Mans, each fitted with a low-drag aerodynamic configuration designed to maximise speed on the long Mulsanne Straight. The race proved difficult. Two of the three entries failed to finish. The surviving car ran as high as second place after 18 hours of racing but was hampered by gearbox problems in the closing stages and crossed the line in fifth position — a respectable result given the attrition, but a disappointment for a car that had shown such dominance in sprint events.
The XJR-8's championship season broke Porsche's grip on the World Sportscar Championship and re-established Jaguar as a serious force in international endurance racing. Its design was directly developed into the XJR-9, which went on to win the 1988 Le Mans 24 Hours — the result the 1987 machine had narrowly missed. One surviving XJR-8 is preserved and displayed at the Beaulieu Motor Museum in England. The car's single-season dominance — eight wins from ten starts — stands as one of the most complete championship campaigns in Group C history.