Founded in 1920 as a commercial high school for young women, eight students were housed in the basement of the St. Bernard’s Girls School on Middle Street in Fitchburg behind St. Bernard’s Church. The need for a Catholic high school in Fitchburg was recognized by Bishop Beaven and plans to build one materialized during the pastorate of Rev. James J. Donnelly.  The first mission in the United States for the Sisters of the Presentation of the Blessed Virgin Mary was to begin this school.

In the spring of 1925 Father Donnelly purchased the Page Estate on the corner of Summer and Harvard Streets.  This house became a convent for the Sisters. Construction of the building on Harvard Street which would become St. Bernard’s High School began in July of 1926. On September 8, 1926 in temporary quarters at the Girls’ School, fifty-four boys and girls began an extended curriculum including Classical Course.

The new high school opened its doors to students on September 4, 1927.  Eight Sisters were assigned to instruct them. A newspaper account of the event stated, “…the new school will occupy a prominent part in the education of the boys and girls of the city in the future.”   In 1953, then Bishop John J. Wright designated St. Bernard's as a regional, diocesean high school. The school would go on to grow quickly in its enrollment and the physical expansion of the school would continue over the decades to include an additional wing built in 1964 containing a chapel, library, cafeteria, three science labs, a language lab, administrative offices and nine classrooms.  St. Bernard’s High School was and continues to be recognized locally, not only for its academic excellence, but also as a fierce competitor in local sports.

Athletic fields were constructed for the school beginning with the school’s football field, known as The Bernardian Bowl in 1946. A state of the art quarter mile track was added in 1964, identical to the one used in the 1964 Olympics. In 1980 the Activity Center opened its doors just one short year after parents and alumni began a half million dollar fundraising campaign to fund the project. The facility contains a 1,000 seat gymnasium, coach’s offices, student athlete locker rooms, and a function hall recently converted to serve as a practice gym.

In recent years the student body of St. Bernard’s High School has hailed from twenty-six different cities, two states and seven countries.  As of 2015, 12,000 men and women have graduated. There is a St. Bernard’s High School graduate living in nearly every state in the United States and in ten countries around the world.  Graduates are prominent in the Church, business, politics, medical profession and service to the country.

St. Bernard’s High School boasts nearly a century of rich, Catholic history and storied traditions and holds steadfast to, “proudly educate its students in a Christ-centered, student-focused, college preparatory environment." By providing a safe and structured academic climate, St. Bernard’s recognizes and promotes each student’s unique gifts and talents, in both curricular and extracurricular realms.  A St. Bernard’s education builds a bridge to the future, while maintaining ties to the school’s rich past. In doing so, St. Bernard’s strives to produce community leaders who embrace the school’s motto: "Love One Another."