Mieres, from Mar del Plata in Argentina, was an outstanding sportsman, excelling in tennis, rugby, rowing and yachting. He participated in 17 Grands Prix, debuting on June 7, 1953. He scored a total of 13 championship points. He competed for Argentina in 1960 Olympic Games sailing in the Star Class.
Born in Mar del Plata in Argentina, Mieres came from a wealthy background and was a natural athlete who excelled at tennis, rugby, rowing and yachting. A broken leg put an end to much of this and he turned to motor sport initially racing an MG with friends at the San Justo Speedway in 1947.
A 7.2 litre Mercedes SSK replaced the MG the following year. He owned a number of pre-war cars including the ex-Varzi Bugatti, with which he won the Argentine sports car championship. In 1949 he was took an old 2.3-litre supercharged Alfa Romeo to Rosario to take part in the support race for the Argentine Grand Prix. Giuseppe Farina and Alberto Ascari were impressed and suggested that Roberto should race in Europe. At the time the Argentine authorities were paying for drivers to go to Europe and he joined Fangio, Froilán and Juan Carlos Guzzi at Varzi's house in Galliate, about 30 km from Milan.
He drove in a number of races with a Gordini and a Ferrari. After taking sixth in Aix-les-Bains, he finished fourth in the Grand Prix des Nations in Geneva driving a Ferrari. However the government stopped the funding and Mieres returned home to compete in local events.
Itching to race abroad again, he went to the United States in 1953 to race a Jaguar at Bridgehampton and then back to Europe having done a deal as reserve driver for Gordini, a deal done through his friendship with Harry Schell. While waiting for a chance to race he went to Italy and to test for Lancia. But though he was quicker that their regular drivers his need to be paid prevented a deal being struck with Gianni Lancia. He returned to Gordini and finally got his chance to race when he replaced the injured Jean Behra at Bordeaux. That year he took part in three World Championship GPs and finished fourth in the non-title Albi Formula 1 race driving the F2 Gordini.
In 1954 Roberto ordered a Maserati 250F, but he started the season with an interim A6GCM/250 (2046). This was a 1953 works car converted by the factory for Mieres. To say that the car had an eventful 1954 season is perhaps something of an understatement. After a retirement in the Argentine Grand Prix in Buenos Aires, he took a fine third in Pau. He then crashed in practice at Bordeaux but took fourth in the International Trophy race at Silverstone a week later. He retired form the Grand Prix at Bari and the Grand Prix di Roma at Castel Fusano at the beginning of June. At the Belgian Grand Prix on June 20th at Spa-Francorchamps he suffered nasty burns when an engine blew up and he was sprayed with burning fuel but he was back on July 6th, heavily bandaged, for the French Grand Prix at Reims. The car was then heavily damaged when the transporter hauling 2046 back to Modena overturned. The transporter was a two tiered and 2046 was on the top. Broken into two big pieces it was effectively written off. Fortunately his new 250F arrived and he immediately took fourth places in both the Swiss and the Spanish Grand Prix.
Maserati signed him up as a works driver for 1955 to partner Jean Behra. He finished on the podium in a number of non-championship races, taking second in the Turin GP and third at both Pau and Bordeaux, and finished fourth in the Dutch Grand Prix, posting the fastest lap in the process.
With the overthrow of Juan Peron back home, Mieres retired from Grand Prix racing at the end of the year to tend his business interests.
Roberto did made a brief return to racing, finishing fourth In the 1957 Buenos Aires 1000 Km in the Ecurie Ecosse Jaguar D-Type. Then in 1958 he raced a Centro Sud Maserati 250 F in the Buenos Aires City GP and shared a works Porsche with Barth and d'Orey in the Buenos Aires 1000 Km, claiming a class win and fifth place overall.
Mieres subsequently raced occasionally in the USA, driving a Porsche at Daytona and Sebring. He also raced an OSCA in the Carrera Panamericana in Mexico and took part in single-seater and saloon car events, with a Volvo, at home and in other odd places, including Puerto Rico, until 1962-63.
In 1960 he was part of the Argentine Olympic yachting team, sailing in the Star Class in the Rome games and in 1963 he decided to concentrate full time on sailing.
In 2004 Mieres returned to racing, trying a J2 Allard at the Monaco Historic event, at the grand old age of 79.
Mieres is from now retired and lives on a farm in Uruguay.