He then pursued further studies at the University of Ceylon, Peradeniya graduating in 1961 with Bachelor of Arts in English literature, western classics and European history.
After joining the Foreign Service he served in India, Germany, Pakistan and Bangladesh before being appointed Ambassador to Yugoslavia (1986–1991) where he was the Dean of the Diplomatic Corps.
During his tenure he had been Sri Lanka’s accredited permanent representative to the UN’s Food and Agriculture Organization (FAO), the World Food Programme (WFP), and the International Fund for Agricultural Development (IFAD) and had served as the chairman of the Group of 77 (G77) Conference as chairman of the Rome Chapter from 1999 to 2002.
Wilhelm would serve as president of the Dutch Burgher Union of Ceylon until suffering from a debilitating stroke and tragic death with his loving wife Desiree Frederick Rita Hills at his bedside.
For those who were fortunate to have the rare honor to have known Wilhelm would know what it was to bask in his generosity, compassion and enjoy his intellectual wit.