Ramponi began his automotive career in Milan, first working for the Florentia car maker and later the Pelizzola company, a manufacturer of fuel pumps. In 1918 he became the personal mechanic of opera singer and accomplished racing driver Giuseppe Campari, who went on to win at Mugello in 1920 with Alfa Romeo. By 1924, Ramponi had risen to the role of chief riding mechanic and co-driver for Antonio Ascari, partnering with him in the formidable Alfa Romeo P2. Ascari was killed in a racing accident in 1925, though Ramponi was not in the car at the time — a rule change that year had eliminated the use of riding mechanics in grand prix events. Ascari died in Ramponi's arms, a moment that left a lasting mark on his life.
Working under the celebrated engineer Vittorio Jano, Ramponi served as test driver for the Alfa Romeo 6C in 1927 and resumed his role as chief mechanic and co-driver alongside Campari. Together they achieved back-to-back victories at the Mille Miglia in 1928 and 1929, one of the most demanding road races in existence. Ramponi also demonstrated strong results in England, winning the 1928 Brooklands Six-Hour race and the 1929 Brooklands Double 12 Hour race, both in the Alfa Romeo 6C.
After losing his position at Alfa Romeo in 1929, Ramponi went to work for the daredevil British driver Tim Birkin and the team operated by the wealthy patron Dorothy Paget. He returned to Alfa Romeo in 1932 to contribute to the development of the Alfa Romeo P3, one of the dominant grand prix cars of its era.
In 1934 Ramponi joined forces with American-born racing driver Whitney Straight as team leader, and together they won the inaugural South African Grand Prix. From 1935 he worked as a mechanic for Dick Seaman, the promising British driver who would go on to race for Mercedes-Benz before his tragic death in 1939.
Ramponi became a British citizen during the 1930s. During World War II he was interned on the Isle of Man as an Italian national, a period during which his first wife died of peritonitis. He married Irene Cooper in 1947. Following the war, he spent approximately twenty years as a consultant to various automobile and aircraft companies. In 1968 he and his wife relocated to South Africa, where he spent his later years.
Giulio Ramponi's career spanned the full breadth of pre-war European motorsport, from the grand prix circuits of the mid-1920s to endurance classics and the emerging scene in South Africa. His work alongside Ascari, Campari, Birkin, Straight, and Seaman placed him at the centre of the sport's most celebrated moments across two decades. His victories at Mille Miglia and Brooklands in the late 1920s stand as enduring achievements in the history of long-distance racing.