| 1849 Dec 21 | The foundation stone was laid in Mutuwal by the First Bishop of Colombo, Rt. Rev. James Chapman. |
| 1851 Feb 3 | The Preparatory School was opened with 50 boys and with Bishop Chapman in charge. |
| 1851 May 21 | Rev Wood arrived and took charge of the College as the first Warden. |
| 1852 | College orphanage opened. |
| 1853 | Warden Wood retires. |
| 1854 | Warden Baly takes charge of the College. |
| 1854 Sept 20 | Christ Church Cathedral dedicated and served as the Cathedral of the Diocese of Colombo and the Chapel of the College. |
| 1860 | Warden Baly retires. |
| 1863 | Warden Bennet assumes duty. |
| 1866 | Retirement of Warden Bennet. |
| 1871 | Rev J Bevan is appointed as the First Sub warden. |
| 1875 | The College Magazine started by the Sub Warden Rev. T.F. Faulkner. |
| 1877 | Warden Bacon retires. |
| 1878 | Rev E.F. Miller appointed as Warden. |
| 1879 | College Library & Debating Society Started. |
| 1884 | College Colours of Blue & Black selected and first used. |
| 1885 | The Nine Run match played & won by STC. |
| 1886 | The OBA formed. Feb 1st named as Old Boys Day. |
| 1891 | Cadet Corps formed. Beginning of Prefect & Detention system. Retirement of Warden Miller. Rev Read assumes duty as the Warden. |
| 1894 | Publication of the First History Book by Mr. C.H. David. |
| 1895 | Retirement of Warden Read. |
| 1901 | Warden Stone takes over the College. |
| 1901 Dec 16 | Golden Jubilee of the College. |
| 1914 | World War I. 88 Thomians killed in action. Lt. Basil Horsfall was awarded posthumously the Victoria Cross for valour. |
| 1917 Dec | College moved out of Mutuwal after 63 years. The Cathedral remained. |
| 1918 Jan 25 | College reassembled in Mt. Lavinia. The Main Block and the Science Laboratory were the only 2 permanent buildings. |
| 1920 | War Memorial committee of the OBA purchases & creates Big Club Ground. |
| 1921 | Choir revived by R.B.W Jayasekera. |
| 1922 | Cub pack formed by Mr. V.P. Cooke. |
| 1923 | Dining Hall built. |
| 1924 | Big Club Grounds opened and dedicated to the those who died in the Great War. |
| 1925 | Warden Stone retires. |
| 1926 | Warden McPherson takes charge of the College. |
| 1926 | Day House System started. |
| 1927 Feb 13 & 15 | Chapel of the Transfiguration dedicated by Rt. Rev. Mark Carpenter Garnier, the Bishop of Colombo. |
| 1929 | The 16th Colombo Scout Troop was formed. Hockey was introduced. |
| 1929 | Foundation stone for the new Dormitory was laid by the Governor of Ceylon. |
| 1930 | The Board of Governors was formed & was incorporated by an act of the legislature. Retirement of Warden McPherson. |
| 1931 | Fives Courts were gifted by Dr. R.L.Hayman. |
| 1932 | Canon de Saram appointed as Warden of the College. He was the 1st Old Boy & Ceylonese Warden. |
| 1934 | The Swimming Bath was gifted by Dr. R.L. Hayman. |
| 1937 | ‘The History of S. Thomas’ College Colombo’ written by Mr. W.T. Keble. |
| 1938 | The Hammond Organ was gifted by Sir Stewart Schneider. |
| 1937 | Beginning of World War II. |
| 1942 | School temporarily closed at Mount. Transferred to Getambe, Milagiriya (St. Paul’s) & Mt. Lavinia (Girls High School) while the College Campus was taken as a hospital. |
| 1945 | The Getambe group became S. Thomas’ College Gurutalawa, which was the first branch school. |
| 1946 | College reassembled at Mount Lavinia. |
| 1946 | The modern Coat of Arms made its’ first debut at the Royal Thomian Cricket Match. |
| 1947 | The Service of Nine Lessons and Carols introduced by Canon R.H.B. Yin. It was styled in the way that of Kings College Cambridge. |
| 1948 | Independence of Ceylon. Rt. Hon. D.S. Senanayake, a Thomian became the 1st Prime Minister. |
| 1951 | The Centenary Year of the College. S. Thomas’ became a Private Fee Levying School. |
| 1951 Feb 3 | Laying of the foundation stone for the Lower School Building. |
| 1951 | Rifle Range declared open. |
| 1955 | Introduction of Rugby Football. |
| 1956 | Introduction of Basketball. |
| 1957 | Military Road named as de Saram Road. |
| 1957 | Retirement of Warden de Saram. |
| 1959 | Warden Davidson assumed duties as the 1st lay Warden. |
| 1959 | Introduction of de Saram house. |
| 1959 Oct 6 | First Observance of the Feast of St. Thomas, the Apostle, the Patron Saint of India & Ceylon. |
| 1960 | The Student Christian Movement was inaugurated for the whole Christian Community of the College by the Rev. Canon R.H.Bower Yin. |
| 1962 | The Ceylon Liturgy first used in the Chapel. |
| 1962 | Retirement of Warden Davidson. |
| 1965 | Rev. Selvaratnam takes charge of the College as the Warden. |
| 1967 | The Post of School Manager introduced by Bishop Harold de Soysa. |
| 1968 | The Mural of the Transfigured Christ finished by Mr. David Paynter. |
| 1969 | Retirement of Warden Selvaratnam. |
| 1969 | Warden Anandanaygam assumes duty. |
| 1974 | Grade 1 classes opened. |
| 1977 | Retirement of Warden Anandanayagam. |
| 1977 | Mr. Illangakoon became the Warden of the College. |
| 1979 | Centenary Royal Thomian Cricket Match played first time for 3 days. |
| 1979 | Hewisi Band formed. |
| 1983 | Warden Illangakoon retires. |
| 1983 | Mr. Neville de Alwis becomes Warden. |
| 1984 | Swimming Pool refurbished and dedicated to the memory of Dr. R.L. Hayman. |
| 1984 | The College Office shifted to the Old Zoo- Botany Lab. Thalassa renovated and become the official residence of the Sub Warden (Upstairs) & Chaplain (Downstairs). |
| 1986 | The Allen Digital Organ installed in the Chapel. |
| 1987 | The C Block declared open in commemoration of the Centenary Anniversary of the OBA. |
| 1988 | The Scout Room declared open. |
| 1990 | The Winchester Dorms & Sick Room declared open by the Lord Bishop of Colombo. |
| 1992 | Phase I of the Indoor Sports Complex declared open by the Lord Bishop of Colombo. |
| 1993 | The 75th Jubilee of the transfer from Mutuwal to Mount. A Jubilee walk was organized in which a sapling of the Banyan tree in Mutuwal was planted in the Chapel Gardens. |
| 1997 | Sports Complex opened by Prof. G.L. Peiris |
| 1998 | The Thomian Chamber Orchestra was formed. |
| 1998 | Retirement of Warden de Alwis. |
| 1999 | Commemorative Stone unveiled & the Big Club Grounds re dedicated for those who died in the Wars. |
| 2001 | The Installation of Dr. Ponniah as Warden. |
| 2002 Feb 3 | The Sesquicentennial Celebrations of the College. A Service of Thanksgiving was held. A bust of Bishop Chapman unveiled by the oldest Thomian Clergyman (Rev. Denley Peiris). The Heritage Museum declared open by the Oldest Living Thomian (Mr. Artie Lankatileke). College General Assembly held in the hall in which a commemorative stamp was canceled by the Warden. |
| 2002 | The Platinum Anniversary of the College Chapel. A service of Holy Communion was held. |
| 2002 | A teacher’s felicitation ceremony was held in connection with the 150th Anniversary. |
| 2002 | A Cub Room was opened. |
