A graduate of civil engineering from the University of Adelaide, Harnden joined the Kinhill Engineers company in 1986. He worked on a wide variety of engineering projects before becoming involved with the management of engineering works for the Australian GP in Adelaide. In 1990 he was appointed track manager for the Grand Prix. His responsibilities included constructing the street circuit every year and making sure that everything met the necessary standards imposed by the FIA.This experience led to him working on the design of the Zhuhai International circuit in China and as a consultant engineer to a Malaysian project for a Formula 1 race. This was later shelved, though the Malaysia GP was eventually held for the first time in 1999. Harnden was also involved in the study for a proposed street circuit in Buenos Aires, Argentina, in 1993.Soon afterwards he was hired by the Grand Prix office in Melbourne. There he did the technical groundwork for the race in Albert Park and was involved in the design of the track. Harnden went through all the inspection processes with the FIA and each year was responsible for setting up the event. He was appointed deputy chief executive to Judith Griggs and replaced her when she resigned from the job in 1998, becoming chief executive of the Australian Grand Prix Corporation at the age of only 32. At the end of 2002 he stood down from his job and moved on to head the organisation for the Commonwealth Games in Melbourne in 2006.