Originally a boys'-only school, St Columba's College announced its move to co-education in June 2020, with the first girls being admitted as pupils in 2021.

In 1955, it was taken over by the Brothers of the Sacred Heart (New England Province) who also purchased the neighbouring Watling House and undertook major construction across the school site.

In 2013, the college completed a major building project, refurbishing the main school hall as-well as introducing new classrooms, meeting and seminar rooms, offices and a Fitness Suite.

Prior to 2005, both the college and the prep had the same four houses, named after four English Catholic martyrs: At the start or the 2005–6 academic year, a new house system was introduced in the senior school, to provide smaller tutor groups for greater personal development of students, as well as to cater for an increase in numbers of students entering.

Pupils remain in their House throughout their time in the Senior school, but have different tutors as they progress to meet the needs of different age groups.