Dernie was brought up in Lancashire and won a place at the famous engineering school at the Imperial College of London University. He worked briefly designing gears for David Brown Industries and then tried his hand at the design of record players with the Garrards company. At the end of 1976, however, he joined the Hesketh F1 team, working on the design of the 308E for the two seasons before the team closed down. By the time that was over he had acquired a taste for the engineering challenges in F1 and soon afterwards found a job with the newly formed Williams Grand Prix Engineering. He became Patrick Head's first aerodynamic assistant and, working in the Imperial College windtunnel in London, helped Head and assistant designer Neil Oatley to produce the Williams FW07. The car made Williams a winning team and Dernie continued to head Williams' aerodynamic activities into the mid-1980s - helping to win three World Championships and playing an important role in establishing the team's own windtunnel facility. Later he designed the Williams active suspension system. In 1989 he was finally lured away with an offer to become Team Lotus's Technical Director, replacing Gerard Ducarouge. Lotus was by then in decline and it hit rock bottom at the end of 1990. Dernie left to take up a similar position with Ligier at Magny-Cours. He remained with the French team for two years but when Guy Ligier sold the operation to Cyril de Rouvre, Dernie went back to England and found a job working with Ross Brawn - who had once been his deputy at Williams. He engineered Michael Schumacher in 1993 but was then sent off to work as technical director of Ligier again after the team was bought by Benetton boss Flavio Briatore. The team was later taken over by Tom Walkinshaw but in April 1996 Dernie moved with Walkinshaw to Arrows. A year later Walkinshaw appointed John Barnard as the new Arrows technical director and Dernie left the team. He joined Lola Cars as technical director with the brief to help rebuild the company after its disastrous F1 program. Dernie left Lola in 2002 and rejoined Williams as a consultant engineer in 2003.