In addition to serving in the ministry, de Silva participated for twenty years in the dialogical and ecumenical activities of the World Council of Churches, and he was Executive President of the Presidium of the National Council for Religion and Peace in Sri Lanka (1979–1980).
Selain menjabat dalam pelayanan, de Silva terlibat selama dua puluh tahun dalam aktivitas dialog dan ekumenikal di Dewan Gereja-gereja se-Dunia, dan ia menjadi Presiden Eksekutif Presidium Dewan Nasional untuk Agama dan Perdamaian di Sri Lanka (1979–1980).