Racing in his private Connaught, he finished in 13th place, but retired from his last world championship race in 1955, after a damaged brake pipe caused him to spin official
He participated in two Formula One World Championship Grands Prix, making his debut on 17 July 1954 at the British Grand Prix. Marr competed in several non-Championship races, with his best results including winning the 1955 Cornwall Medical Research Council Formula 1 Race and finishing fourth in the New Zealand Grand Prix the following year.
He is also an artist, having studied at the Borough Polytechnic (later London South Bank University) under David Bomberg and as a member of the Borough Group.