Ewy Rosqvist was quick to become a competitive racer, and after a while she was one of Europe's best female drivers. In 1960, she signed as a factory driver for Volvo. Two years later, Mercedes Benz bought out her contract, starting her international career in earnest. During her most intense years of competition, she could have as much as 280 travel days away from home.
She won the European Championship in 1959, 1960 and 1961, the latter shared with Pat Moss.She won the ladies' classification in Midnattssolsrallyt ("Rally to the Midnight Sun", now called Rally Sweden) from 1959 to 1962.
In 1962, Ewy Rosqvist successfully participated in the Argentine Grand Prix race Gran Premio de Argentina (as the first female), she drove a large Mercedes-Benz 220 SE with Ursula Wirth co-driving. The duo won all six stages and also set a new speed record for the race. In 1961 the average speed of the winner was 121 km/h, Rosqvist's average in 1962 was almost 127 km/h.
In the following years, Rosqvist placed second and third (in 1963 and 1964 respectivelyin the Argentine GP, as well as victories in the 2.5-litre class in both the Monte Carlo Rally and on the Nürburgring. She also participated successfully in the Acropolis and Spa-Sofia-Ličge rallies.
Rosqvist stopped participating in large races races after Mercedes-Benz disbanded their factory rally team in 1965. By then, new manufacturers with lighter cars had made the relatively heavy Mercedes much less competitive. Ewy Rosqvist got an offer to drive for Audi, but instead chose to end her career in top-tier racing. In June 1964, she married Alexander von Korff, head of the Mercedes-Benz motorsport division.
Ewy Rosqvist stopped competing in 1967, after a career completely without accidents, crashes or broken cars. Her trophies and race car are displayed at the Mercedes-Benz Museum in Stuttgart. She worked for many years at the museum as a guide and was a test driver for new Mercedes models.
Rosqvist remained for several years in Stuttgart after Alexander von Korff died in 1977, but eventually moved back to Sweden. There she met Karl Gustav Svedberg, head of the company Philipson Bil AB, an importer and dealer of Mercedes-Benz automobiles.They lived together until his death in 2009.