John Hung's maternal grandfather was Sir Robert Hormus Kotewall and he is the step-son of M. C. Hung, who was the last compradore of Jardine, Matheson & Co. He went to Pui Ching Middle School for the purpose of learning Chinese.
Hung held posts with various Wheelock-owned companies, including Cable TV Hong Kong (vice-chairman) and Cross-Harbour Holdings (executive director). He also served as chairman of the Hong Kong government's Sports Development Board. He was awarded a Silver Bauhinia Star in 1999. He retired in 2002. Following his retirement, he continued to work as a consultant.
In November 2008, Hung was arrested by Independent Commission Against Corruption officers outside of the Conrad Hotel at Pacific Place. In June 2009, a court found that Hung had accepted a HK$450,000 bribe in exchange for his support of Joanne Wong Pui's application for full membership in the Hong Kong Jockey Club, convicting him of one count of soliciting an advantage and three of accepting an advantage. He was sentenced to two years in prison and ordered to pay HK$350,000 to the HKJC; the judge gave him a mild sentence in light of his age and his "past contributions to Hong Kong". He filed an appeal to have his conviction overturned; however, it was denied. The Court of Appeal stated that there was "ample evidence" of his guilt.
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- Moy, Patsy (2009-06-26), "Ex-Wheelock boss jailed for graft", The Standard, retrieved 2010-03-31
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- Ho, Maggie (2010-07-08), "'Ample evidence' of John Hung's guilt", RTHK, retrieved 2010-08-17