Although Gregory revealed its class in numerous formula 1 race, were his real strengths in sports car racing. The bespectacled American had as heir to an insurance company with the necessary capital to afford racing car can. Gregory began in 1952, influenced by his brother, with motor racing. At first he denied race at Jaguar; His first international appearance was in 1954, the 1000 km of Buenos Aires. After the race, he earned the victorious Ferrari there and also started in Europe to race. In the following years he won races at Aintree and Nassau and finished at numerous other race podiums. His biggest success so far was winning the 1,000 km from Buenos Aires in 1957, along with Eugenio Castellotti and Luigi Musso.
After he had convinced these races, he was made available for the 1957 Formula 1 season a Maserati. In his first race, the GP of Monaco, he was third. Together with two fourth places showed the Rank 6 in the championship, and the first in his year. In the season of 1958, he entered Maserati also sporadically, but only achieved a fourth place in Italy. For him victory compensated for sports cars race on the AVUS in Silverstone and Spa-Francorchamps.
His best Formula 1 season was the year 1959, in which he was a Cooper - Climax second in the Portuguese Grand Prix and third in the GP of the Netherlands. In Germany he retired in leadership from lying. In the following years increased its Formula 1 career, but he celebrated 1961 Maserati a victory at the 1000 km race at the Nürburgring.
Mid- 1961 he moved to a Lotus privateer team, where he remained for the next two years. With inferior car he could not play his class, a single championship point (6th place at the GP of USA 1962) remained his meager yield. Even a victory in a World Cup not counting race in Karlskoga (Sweden) can not hide. End of the season in 1963, he joined for two Grands Prix on Lola, but different from both times.
Gregory paused a year, and returned in 1965 fulminant. In the 500-mile race at Indianapolis he tried his first time this year. Starting from the rear seats he worked his way gradually up to fifth place before, as threw him an engine problem out of the race. Only a few weeks later, he won with Jochen Rindt on a NART Ferrari, the 24 - hour race at Le Mans. His Formula 1 career he finished after a few feeble attempts to BRM The end of 1965, but remained active until 1972 as a sports car racing driver and was able to achieve more good results.
Gregory retired to Amsterdam, where he began a second career as a diamond dealer and jeweler. Died in 1985 the chain smoking during an Italy vacation until the age of 53 of a heart attack.