Brother Conrad Cassidy was born in Chippewa Falls, Wisconsin, July 31, 1909, the only child of Andrew and Elizabeth O'Connell Cassidy. The family moved to Minneapolis, Minnesota, where Conrad completed his grade school and high school education. In 1937 he entered the Dominican Order and received the habit at the Dominican House of Studies, River Forest, Illinois. Early in his religious life he was assigned to Fenwick High School, Oak Park, Illinois, where he served as sacristan. He also wrote poetry in his early years. Four years later he was assigned to St. Pius Priory, Chicago, Illinois, where he worked in the print shop of the Shrine of St. Jude Thaddeus. After seventeen years in this position he returned to Fenwick High School, where he oversaw the security of both the school and the priory.

When the Dominican community of St. Dominic Priory at Fenwick moved to St. Thomas Aquinas Priory (the House of Studies) in River Forest, Brother Conrad joined them there. During his later years he was afflicted with severe diabetes and moved into the assisted living facility at St. Thomas Aquinas Priory. After being admitted to Oak Park Hospital with chest pains, he was stricken with a massive heart attack and died on September 14, 1994. A Mass of Christian Burial was celebrated at St. Thomas Aquinas Priory on September 17, 1994, and he was buried in the Dominican plot at All Saints Cemetery, Des Plaines, Illinois.