Marimon began his racing career in 1951, aged just 19, encouraged by his father and by his great friend and fellow Argentinian and Maserati racer Juan Manuel Fangio.

Along with his fellow countryman, Frolian Gonzales, Marimon moved to Europe in 1951, where he raced in the Le Mans 24 Hours behind the wheel of a Talbot. He made his debut in the F1 World Championships at Reims, driving a Maserati, but was forced to pull out after just two laps.

Nicknamed "Pinocchio" because of his resemblance to Collodi's famous puppet brought to the screen by Walt Disney, Marimon proved to be one of the most promising drivers of 1953, winning third place in an A6GCM in the Belgian Grand Prix. In the same year, he also raced in the Swiss Grand Prix (on the Bremgarten circuit) and in the Italian Grand Prix, where he managed to keep up with the drivers in the lead despite being lapped because of technical problems. His friend, Fangio, won one of the greatest victories for Maserati in this race, getting the better of Alberto Ascari and Giuseppe Farina in the last corners.

Marimon became an official driver for Maserati in 1954, winning the Rome Grand Prix (which was not part of the F1 World Racing Championship circuit) and an impressive third place in the British Grand Prix, behind the Ferraris driven by Gonzales and Hawthorn and ahead of Fangio in his Mercedes W196.

Sadly, the apparent fairy tale came to an abrupt end when the unlucky champion had an accident during a practice session for the German Grand Prix at the Nurburgring. The wheels of his single-seater locked in the downhill descent to the Adenau bridge and the Argentine lost control. He was killed outright, aged just 22.