The Thomian choir is one of the oldest institutions of the College. The choir rst sang on St. Mathew’s Day, on September 21st 1854 at the dedication of the Christ Church Cathedral, which served as the Chapel of S. Thomas’ College Mutwal. Since then the choir has earned itself a venerable place in the history of the College. The choir stalls which are now in use were given in memory of Archer Dias and Eardley Dias in 1951, by their mother. The story is told that when the stalls were given in the making, Rev’d Roy Yin, the Chaplain at that time, who apart from the fact that he was an inspiring choir master, mathematician par excellence and the half-brother of Leslie Charteris of “The Saint”, did not agree with the carpenters as to the size of the stalls. On the completion of two of them, the Chaplain knelt at one of them and found that he was mistaken. The other two were made according to the specications of the carpenters. This is why, they say, the choir stalls are of two sizes.
The Chapel has developed a reputation for high standards of Choral and Liturgical excellence with a renowned choir contributing in no small measure to this reputation. The Chapel choir is afiliated to the Royal School of Church Music in London. The Chapel has always been ‘High’ in its pattern of worship and it is this heritage of Anglo-Catholicism and the emphasis on Traditional Anglicanism, which continues to nurture the young Thomians of today. The contributions of men like Rev’d Gilbert, Prof. R.B.W. Jayasekera, Rev’d Foster, 
Budd Jansze, Rev’d Roy Yin, Rev’d L.G.B. Fernando, Mr. Russel Bartholomeusz and the late Mr. Vinodh Senadeera have been in building up the choir to what it is today. Currently the choir is trained by the Sub Warden, Mr Asanka S. Perera.
A most important event in the College as well the Chapel calendar is the Service of Nine Lessons and Carols, which was introduced by Rev’d Canon R.H.B. Yin. The first carol service was held on the 7thof December 1947. Even up to the present this service, which is styled on the basis of that of King’s College Cambridge England is held on the First Sunday in December every year. It is truly a service of praise and thanksgiving for the Thomian voices to God and for sending his only begotten Son Jesus to save the world.
In the year 2012, a choir fund was begun in memory of Rev’d Roy Yin to whom the school community and the choir owe much. All proceeds are utilized to provide the choir better facilities and opportunities. As a result, the choir was invited to sing in Dubai and Sharjah during the Holy Week in 2014. In the same year, the choir of Jesus College Cambridge joined the school choir in the Chapel for a service of Advent lessons and carols.
The choir is solely for the worship in the College Chapel and therefore refrains from performances. Moreover, it is recorded solely on permission of the Warden of the school. The choir has recorded and released a collection of choral music ranging from Advent to Lent to mark its 70th Festal Service of Nine Lessons and Carols and the 90th anniversary of the Chapel of the Transfiguration in 2017.