Simon serves on regional and international bodies, including the ASEAN network of institutes of strategic and international studies (ASEAN-ISIS), the ASEAN Regional Forum on security in the Asia Pacific, APEC and the WTO, and has coordinated a think-tank on Liveable Cities for Philips.
He has published internationally and taught at Harvard Law School, Yale and the Fletcher School. His 2009 book Asia Alone: The Dangerous Post Crisis Divide from America was favourably reviewed in the Economist and Financial Times. He has also written five books of stories and poems, including a Singapore Literature Prize novel, City of Small Blessings.
Simon has served as an independent, non-elected Member of the Singapore Parliament (1997-2001) and chaired the National Environment Agency (2002-08). He also initiated and ran Singapore Volunteers Overseas (1991-93) and led major Singapore public consultations including on the National Green Plan and the City Concept Plan.