John W. Shanahan, the third bishop of the Diocese of Harrisburg, and is the only archdiocesan secondary school in Chester County.

The school was located on the grounds of St. Agnes Parish in downtown West Chester, Pennsylvania, and was run by the Sisters, Servants of the Immaculate Heart of Mary (I.H.M.).

The town's local Knights of Columbus council donated a nearby parcel of land, and ground was broken in 1956 on the new building, which would open one year later.

The rise in population resulted in a dramatic increase in enrollment at Bishop Shanahan, which was the only archdiocesan high school in the county.

[9] When the new building opened, enrollment continued to grow, and a two-story expansion was completed in 2001 to provide 14 additional classrooms, bringing capacity up to 1,600 students.

[12] Bishop Shanahan's most recent graduating class of 2024 amassed a total of over $53 million in scholarship awards from colleges and universities.

The current athletic director of Bishop Shanahan is Paul Meyers, who also serves as the school's head football coach.

[16] On April 25, 2023, the Bishop Shanahan boys' lacrosse team defeated Oxford Area High School, 11–1, earning Shanahan's head coach Jon Heisman his 513th win as a head coach, a Pennsylvania high school lacrosse record.