The school has students in grades 9–12 and offers a wide range of academic and extracurricular activities.

[citation needed] The school colours are green and yellow, and its motto is Nil sine fide et labore, which is Latin for "Nothing without faith and work."

Archbishop Denis O'Connor Catholic High School was founded by Father Leo J. Austin and was officially opened in September, 1964 in Whitby, Ontario.

On November 18, 1984, it was officially opened and blessed by Cardinal Carter.

[citation needed] In 1991 a major addition was constructed which increased its capacity to approximately 1,000 students.