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St. Edmund Campion Secondary School opened with 250 grade 9 students on September 2003 at a holding school in Streetsville.  The school was housed at there for two years, awaiting the completion of their new school at 275 Brisdale Drive. 

For a time Campion shared the Streetville facility with the grade 9 class of St. Marcellinus Secondary and all grades of John Cabot Secondary School.  The schools were only distinguished by their school sweaters. 

Campion's building was completed in 2005 and by then the student population had doubled to 1300 students.  The school housed grades 9, 10 and 11 along with a teaching staff of eighty-five.  On June 8, 2006, Campion's school blessing took place and at that time, the student population was more than 1900.

The school is named after one of the English martyrs, Edmund Campion (1540-1581).  Born to Catholic parents who became Protestants, Campion became convinced that the Catholic Church has the true faith.  He gave up a promising career at Oxford University and an invitation to enter Queen Elizabeth I's service to become a Jesuit and an itinerant priest, who ministered to Catholics in a period of persecution.  In 1581 Fr. Edmund Campion was caught by a priest hunter and executed for being Catholic. 

Like its namesake, Campion seeks to make an impact.  The chaplaincy department has a strong PEACE Team (Peers Evangelizing and Connecting Everywhere), which organizes liturgical celebrations, volunteers to go to local retirement homes and food banks, assists in in food drives, clothing drives, and other school-wide charitable initiatives.  In one campaign, Youth for Christ Campion gathered donations of food and clothing to assist victims of a massive flood in the Philippines.