In 2006 the ethnic composition of St Thomas of Canterbury College was New Zealand European/Pākeha 72%, Māori 7%, Samoan 3%, Other Pacifica 1%, Asian 13%, Middle Eastern 2% and Others 2%.

Academically, the school offers for senior years the National Certificate of Educational Achievement assessment system (NCEA).

The College has an enrolment scheme "to avoid overcrowding, or the likelihood of overcrowding" that gives priority of enrolment to students if they meet the defined criteria of connection with the Catholic faith and live within the Catholic Parishes of Sockburn, Hornby and Darfield, Riccarton, Hoon Hay and Halswell, Leeston, Lincoln and Akaroa.

Eventually Brother Marlow, the Provincial of the Christian Brothers, and Edward Joyce, the fourth Catholic Bishop of Christchurch (Bishop 1950–1964), agreed, and St Thomas of Canterbury College held its first classes on 6 February 1961 (Waitangi Day – not a public holiday then).

The school expanded its area when eight acres was acquired on the other side of Middle Park Road to be used as sports fields.

[9] The New Zealand Herald commented that this was remarkable as St Thomas of Canterbury College was a new school and it was only the third year that it had an upper sixth form).

The dome was removed on 26 July and Catholic Cathedral College moved back to its own site on 1 August 2011.

The Jubilee Mass was celebrated by Bishop Barry Jones of Christchurch on Sunday 9 October in the St Thomas of Canterbury College hall.

[15] As proprietors of the college, the Christian Brothers continued to appoint their representatives to the board under the Private School Conditional Integration Act 1975.