Carlos O. Arzani was born in Ciudad de Buenos Aires, Argentina. He raced mostly in Argentina between 1936 and 1939 in various domestic formule libre races and a few international events.
He entered the 500 mile race at Rafaela in September driving an Alfa Romeo 2900 GP which had been converted to single-seater configuration. He spent much of the race wheel to wheel, swapping the lead with Ernesto Blanco in his Reo. Unfortunately Arzani retired and Blanco went on to take the win. On October 18th he won the Formula Libre Gran Premio Ciudad de Buenos Aires, beating Carlos Zatuszek and Luis Brosutti in Mercedes SSK's and Manoel de Teffé who came home fourth.
In 1937 with the depression almost over in his homeland, Arzani traveled to Europe where he acquired the Ex Scuderia Ferrari 1935 Alfa Romeo Tipo 8C 35, chassis and engine number 55014. Arzani raced it in Naples finishing 4th before taking the car back to Argentine where he embarked upon an ambitious career taking numerous victories and a number podium finishes. By 1951 the car had been significantly modified and had very few Alfa Romeo parts left. The car was further destroyed in a fatal accident in 1948. The original chassis and engine were later reunited and with piles of spares, two cars were built both claiming to be the ex-Arzani 8C-35.
He took a number of wins in 1937 including the Gran Premio de Mar del Plata at La Tablada and the Gran Premio de La Plata at El Bosque. He came 5th in the Grande Prêmio da Cidade de Rio de Janeiro at Gâvea after a race long duel with the Portuguese driver Vasco Sameiro's Alfa Romeo 8C before taking another two wins at San Isidro and the Circuito de Parana.
In March of 1938 he raced in the Ciudad de Necochea. This was notable for being Fangio's first official race. The race was run as two eight lap heats with a fifteen lap final. In qualifying Fangio was fifth and finished a respectable 7th beating some quicker cars however nothing could match the 330 hp of Arzani's Alfa Romeo 8C 3800 and he won easily. In April he won in Parana and in June he was leading the Grande Prêmio da Cidade de Rio de Janeiro at Gávea when it started to rain. On worn tires his pace dropped and he was passed by Carlo Pintacuda who went on to win in his Alfa Romeo Tipo 8C-308. Arzani came second some six and a half minutes later. It was Pintacuda's second win in a row at the Devil's Springboard as Gávea was known. He took another win in August at the Gran Premio de Rosario.
Another win at Parana followed in 1939 and Arzani backed this up with two more wins at the Gran Premio ACA Ciudad de La Plata and the Gran Premio de Rosario.
Suffering from ill health he escaped the summer heat by moving up to the Andes. There he died in a quite mountain village near Rio Ceballos in 1952. His son who is also called Carlos Arzani is an Argentine diplomat.