Marr was born in Durham and studied under Bomberg at Borough Polytechnic after serving in the RAF during World War II. Many ex-service men attended the classes, including (briefly) Joe Tilson, who also served in the RAF. He exhibited alongside other students from the Borough Polytechnic at the Everyman Cinema Exhibition of 1947, an event encouraged and supported by Marr’s friend, Jim Fairfax Jones who was the cinema’s proprietor. After Holden ceded the presidency of the Borough Group to Bomberg, it was enlarged and Marr began serving as the Group’s first Secretary. From 1948 the Group had a permanent rolling exhibition at Marr's bookshop, The Bookworm in Newport Court, Soho.
Marr’s connection with Bomberg was further enhanced through marriage to Dinora Mendelson, Bomberg’s step-daughter. The marriage ended in 1950. Marr also provided Bomberg with significant financial support, funding the trip that the artist and his family made to Cyprus. Marr accompanied Bomberg and his family on the successful painting trip to Cornwall in 1948, indeed it is hard to overplay Marr’s support to Bomberg in the elder artist's later years. His work is characterised by its rich expressionist brushwork and colour palette. Marr is unusual in combining his artistic practice with a brief but successful career as a Formula 1 racing driver, participating twice at the British Grand Prix (1954 and 1955) and winning other events.