Archbishop Williams' school seal, originally that of the founding order of nuns, is the pelican, which was an early Christian symbol of Jesus.

The school's motto is Caritas Christi Urget Nos, or "The Love of Christ Drives Us On."

Archbishop Williams High School was dedicated on September 12, 1949, by Cardinal Richard Cushing.

In February 2004, the school was renamed Archbishop Williams High School Inc. to reflect its new independent governance status after separating from the Boston Archdiocese in the wake of the child sex abuse scandal.

In the fall of 2016 Archbishop Williams unveiled its new Al and Rita Nazzaro P’75, ’76, ’78, ’82, ’83 Science Lab located on the top floor of the school as well as the Paul L. Dignan ’55 Athletic Training Center, its new training and workout center located underneath the gym.