- Aeronautical Society
- Art Club
- Association of Innovation and Design
- Association of Science and Technology
- Automobile Club
- Buddhist Students’ Association
- Canto Perpetua Choir
- Carnatic Orchestra
- Classical Music Association
- Commerce Society
- Cubing Society
- Culinary Arts Society
- English Drama Society
- English Lit & Debating Society
- Gavel Club
- Geography Society
- Health Club
- Hewisi Band
- Hindu Students’ Union
- Histoarcheo Club
- HNB Students’ Savings Unit
- ICT Society
- Interact Club
- Islamic Society
- Junior English Lit & Debating Society
- Junior Maths Society
- Junior Science & Technology
- Kennel Club
- Media Unit
- Photographic Club
- Political Science Society
- Productive Citizenship Society
- Quiz Club
- Scuba Diving Unit
- Radio Club
- Red Cross Society
- Road Safety Patrol
- Senior Environmental Club
- Seylan Bank Students’ Savings Unit
- Sinhala Literary & Debating Society
- Society for Social Work & Welfare
- Spelling Union
- Student Christian Movement
- Tamil Drama Society
- Tamil Literary and Debating Society
- The Ternion
- Thomian Union
- United Nations Club
- Western Band
- Wildlife Society
Cubing Society
Cubing helps improve memory & problem solving skills, makes one’s reflexes faster and keeps the mind active. Thus, the Cubing Society of S. Thomas’ College was established during the Michaelmas Term of 2017 to encourage young cubing enthusiasts to take up speed cubing as a hobby. Since then, we have been teaching the basics of speed cubing to many a young Thomians, and organize informal intra-club matches between the members to improve their skills.