Kua was born in Batu Pahat, Johor, Malaysia, the sixth of seven children. He studied medicine at the University of Malaya from 1968 to 1973, receiving an MBBS degree. After graduating, he was conscripted into the Malaysian Armed Forces to be an army doctor during the Second Malayan Insurgency. He served for two years before returning to Johor to open a clinic. However, he was convinced by a friend to go abroad to travel. He enrolled into the University of Manchester to undertake a Master of Medicine, initially planning to specialise into pediatrics. He later specialised into psychiatry after working at a hospital and elderly home in the United Kingdom.