The son of a truck driver, Murphy built his own motorcycle in his teens but left school at 16 without many qualifications and became a draughtsman in a local business which produced industrial shutter doors. He bored quickly of that and, being keen on cars, started working as a mechanic at a local garage. After a spell when he was a door-to-door insurance salesman in Germany (targeting the British Forces based there), he went back to the drawing office. By then he had started going to races and eventually enrolled for a driver training course with Team Touraco at Cadwell Park and had a huge accident while trying to drive too fast. He started working as a mechanic for Team Touraco's Graeme Glew before getting a job as a race mechanic with the Maurer Formula 2 team on Beppe Gabbiani's car.At the end of the 1982 season he was taken on as a draughtsman at Maurer, working with designer Paul Brown. The team struggled through the year with drivers Stefan Bellof, Alain Ferte and Kenny Acheson and then split up with the designers doing some work in 250cc motorcycle racing. Brown and Murphy then joined a carbon fiber manufacturer in Inverness and designed a variety of curious objects, including electric guitars, rocket-launchers and a CanAm car, which was known as the RK-March 847 and driven by Jim Crawford with some success.Brown and Murphy then joined Zakspeed to design the Germany company's first F1 car which was driven by Jonathan Palmer in 1985. The designers then designed the Ford IMSA GTP car and Murphy spent the year in the United States, engineering Klaus Ludwig. In late 1986 Brown left and Murphy was asked to design the Zakspeed 871 in which Martin Brundle drove on to score Zakspeed's first point in 1987, while Murphy engineered Christian Danner's car.The following year he joined Lola to work with Australian designer Ralph Bellamy on the design of the Lola LC88 for the Larrousse Calmels F1 team. This was followed by the Lola-Lamborghini LC89 and the Lola-Lamborghini 90, the latter car being quite successful. As a result Murphy was hired by Leyton House Racing in mid-1990 to replace Adrian Newey. He designed the Ilmor-engined CG911 but this was very unreliable and in April 1991 Gustav Brunner was appointed over Murphy's head. At the end of the year he left to join Team Lotus which was being revitalized with a new management. There was not much money and the Lotus 107 and 109 models were never able to fulfill their potential with drivers Mika Hakkinen, Johnny Herbert and Alex Zanardi. When the team closed at the end of 1994 Murphy went to America to engineer Scott Pruett at Patrick Racing, a relationship which resulted in victory in the Michigan 500. He returned briefly to Lola in 1996 but was convinced that the F1 program would be a disaster and stayed away from it.In 1997 he became chief engineer of the Astromega Formula 3000 team while also running his own freelance design business. The relationship with Astromega resulted in wins for Soheil Ayari in Helsinki in 1997 and three victories for Gonzalo Rodriguez in 1998 and 1999.