Swimming was introduced to the College in 1934. At first, all practices and training was conducted at the S.Thomas’ College Pool at Mt. Lavinia. Later the St. Joseph’s College pool and the Sinhalese Sports Club pool were used. Although a pool for the school was suggested in 1935, the school built its swimming pool only in 1968. Since then swimming, diving and water polo have grown in popularity among the students.

The main trophies are the J.M.Kersvill shield which is awarded to the overall champions at the Sri Lanka Schools Swimming Championships and the J.C.A.Corea shield awarded to the champions at the annual Royal-Thomian Swimming Championships. The Royal College swimming team is at the frontline among other competitors with consistent top 3 performances at the annual Public Schools meet during the past few years.