After completing his Ph.D., Clark went to the United Kingdom where he was a Harwell Fellow at the United Kingdom Atomic Energy Authority from 1969 to 1972.
Returning to Australia, he was a Principal Research Scientist at the CSIRO Division of Mineral Physics from 1973 to 1980.
While there, he also took on the role of Visiting Principal Scientist for Oak Ridge National Laboratory, United States Atomic Energy Agency from 1976 to 1977.[6] In his research, Clark made significant contributions to the field of mineral physics, particularly in the areas of high-pressure physics and geophysics, phase transformations and crystallography. He also conducted research in the area of diamond anvil cells, which are devices used to study materials at very high pressures.[7]
He bombarded materials with nuclear particles to find new information about their properties, including determining the location of trace elements in mineral grains, deficiencies of chromium in human blood, the quality of uranium ores, the structure of solar absorber surfaces, properties of semi-conducting materials, and trace analysis of air pollutants. From 1980 to 1993, Clark worked as director of science and technology (Australia) and research scientist at the IBM Research Division, Yorktown Heights, in New York before developing a business management career.[8][6]
After completing his research roles, Clark broadened his roles in business senior management. In 1993, he joined News Corporation, a multinational mass media company. At News Corporation, Clark served as the president of technology, where he was responsible for transforming its assets for program creation and media delivery from analogue to digital platforms, across film, print, and television. Clark then moved on to become the president and chief operating officer of Loral Space and Communications, the world's largest commercial satellite manufacturer. During his tenure, he was credited with turning around the struggling company and making it profitable. Clark also served on the board of the ANZ Banking Group, one of Australia's largest banks, from 2004 to 2013.[1] He founded and served as the chairman of KaComm Communications in 2006, a company that provided satellite-based communication solutions to businesses and governments around the world.[6][9][4][5]
In addition to his corporate roles, Clark has had active roles on the boards of diverse public and professional service organisations. These include serving on the National ICT Australia Review Board since 2006, being on the council of the Royal Institution of Australia since 2010, chairman of the advisory board to the A.R.C. Centre for Ultrahigh Bandwidth Devices for Optical Systems since 2011, a Councillor at the University of Sydney Physics Foundation since 2013, chairman of the Commercial and Philanthropic Development Board, Australian National University's School of Physical Sciences and Engineering since 2013, and a board member at Questacon National Science and Technology Centre since 2014.[3][6]
