Selwyn Edge's victory for Britain in the 1902 Gordon Bennett Cup passed hosting rights to the Automobile Club of Great Britain and Ireland. Motor racing on public roads was illegal in mainland Britain, but Claude Johnson, the club's secretary, proposed Ireland as the venue. Richard J. Mecredy, editor of the Dublin Motor News, suggested County Kildare. To enable the race, special legislation — the Light Locomotives (Ireland) Bill — was passed on 27 March 1903. Local authorities were canvassed widely; 102 Irish MPs, 90 Irish peers, 300 newspapers, 34 county council chairmen, railway companies, hoteliers, and ecclesiastical figures were contacted for support. The Bishop of Kildare and Leighlin Patrick Foley declared himself in favour, and the county was selected partly because straight roads were deemed a safety asset.
The backdrop was critical. The 24 May 1903 Paris–Madrid race had sent more than 200 cars over 800 miles of open roads and had to be halted at Bordeaux after numerous fatalities. The carnage made it impossible to continue city-to-city racing on open roads, and the 1903 Gordon Bennett organisers moved decisively to a closed circuit. The circuit was marshalled by 7,000 police officers, troops, and club stewards, with explicit instructions to keep spectators away from corners.
The Athy Circuit was a figure-eight arrangement of two closed-road loops. The larger loop, 52 miles, ran through Kilcullen, The Curragh, Kildare, Monasterevin, Stradbally, and Athy. The smaller loop, 40 miles, ran through Castledermot, Carlow, and back to Athy. The race covered seven laps — alternating six laps between the two loops before a final lap on the longer circuit — for a total distance of approximately 527 km (327 miles). Competitors were started at seven-minute intervals and required to follow bicycles through controlled town zones. Ninety-one chronographs supplied by Anglo-Swiss firm Stauffer Son & Co. of La Chaux-de-Fonds were used for official timing.
As a tribute to their Irish hosts, the British team chose to race in shamrock green. This established what became known as British Racing Green, a colour that would become synonymous with British motorsport for decades. The 1902 winning Napier had been painted olive green, but the deeper shamrock shade adopted for 1903 became the definitive hue.
Four nations entered: Britain (defending), France, Germany, and the United States. France nominated Rene de Knyff and Henry Farman in Panhards. Germany entered Camille Jenatzy in a Mercedes along with two other cars. Each country was limited to three entries.
Jenatzy drove a Mercedes that was considered inferior in outright horsepower to some of its rivals but suited his driving style. He turned in a dominant performance, winning in six hours and 39 minutes at an average speed of 79.2 km/h (49.2 mph) and earning a purse of £8,000. De Knyff finished second and Farman third, both driving Panhards for France, each completing the course approximately 10 minutes behind Jenatzy.
Germany's victory transferred hosting rights to the Automobilclub von Deutschland for the 1904 edition. The race's significance extends well beyond the result: by demonstrating that a large, internationally attended motor race could be run safely on a closed circuit, the 1903 Gordon Bennett Cup pointed the way for the sport's entire future. All subsequent Gordon Bennett races and the Grand Prix that succeeded the series were held on closed or specially controlled circuits. The closed-circuit format adopted out of necessity in 1903 became the defining structural feature of organised motor racing for the next century.