William Powers Morrissey was born an only child to Lewis and Thrascilla (Powers) Morrissey on January 27, 1936, in Madison, Wisconsin. William attended grammar school at St. Sebastian in Milwaukee, Wisconsin. He received his diploma from Marquette University High School in Milwaukee in 1953. He began undergraduate studies at Loras College in Dubuque, Iowa. After two years of coursework, William entered the Dominican Novitiate at St. Peter Martyr Priory in Winona, Minnesota. He received the habit on August 30, 1955, and the religious name Daniel. On August 31, 1956, Daniel professed first vows at St. Peter Martyr Priory in the hands of V. Rev. John Marr, OP. From 1956-1959, he was assigned to St. Thomas Aquinas Priory in River Forest, Illinois, to study philosophy at Dominican House of Studies. After professing solemn vows in 1959, he was assigned to St. Rose Priory in Dubuque, Iowa, where he studied theology. He was ordained to the priesthood at St. Rose Priory on June 2, 1962, by Most Rev. James Byrne. 

After ordination, Fr. Dan was assigned to St. Pius V Priory in Chicago, Illinois, where he worked part-time in the parish and taught theology at St. Xavier College. In 1964, he began advanced studies in Paris. In 1966, he obtained a Diploma of a Master of Religious Education from the Institut Superieur de Pastorale Catechetique and began doctoral work. He completed all required courses and comprehensives. While there, he became involved with diplomatic work through R. Sargent Shriver, US Ambassador to France. In 1970 he moved to New Hampshire for a position as religion instructor and assistant minister at The Phillips Exeter Academy, becoming School Minister in 1971.  During the summers, he taught at Loyola Institute of Pastoral Studies in Chicago, Illinois. 

In 1979, Fr. Dan was appointed Director of the Catholic Center of the Tulane University and Pastor of St. Thomas More Parish. The following year he moved to New York where he studied for one year at Columbia University before taking a position at Union Theological Seminary. In 1983, he began working for The Dalton School as their Ethical Education Consultant. After a brief stint at Vista Sandia Hospital in Albuquerque, New Mexico, he accepted a position at Columbia Medical School as spiritual director for their students in 1986. He established a program for assisting impaired medical students which gradually expanded to cover issues a broad range of issues (substance abuse, eating disorders, domestic violence, etc.). His work grew to include the School of Dentistry and then the School of Public Health, where he taught as a faculty member. This period was not without controversy as Dan frequently preached in protestant churches, most especially in the Cathedral of St. John the Divine. 

Dan continued to rise through the administrative ranks at Columbia, eventually becoming Assistant Vice President of the Columbia University College of Physicians and Surgeons while continuing his spiritual chaplaincy to students of various faiths. He served on various national medical boards. The class of 2004 bestowed him with its Distinguished Service Award. He retired in 2008 and moved into the residence of Anne Power Werner, a friend from his time in Paris, in North Hampton, New Hampshire. He attended several provincial assemblies over the next decade. In June of 2024, he moved to assisted living at Webster at Rye in Rye, New Hampshire. He passed away there on December 20, 2024, after a brief bout with cancer.