Dennis Chanmugam attended S. Thomas' College, Mount Lavinia, captaining the cricket team in 1967-68. An opening bowler, he played most of his first-class cricket for Sri Lanka on three tours: to Pakistan in 1973-74, to England in 1975 for the World Cup, and to India in 1975-76. Apart from one match against Pakistan in 1973-74 he did not play in the international matches on these tours. His best first-class figures were 3 for 32 and 4 for 60 against Pakistan Universities at Rawalpindi.