Danylak was born in Toronto, Canada. He was ordained to the Catholic priesthood in 1957 and ministered to Ukrainian Catholics in Canada. He received a licentiate of sacred theology from the Pontifical Urbaniana University and a doctorate of canon and civil law from the Pontifical Lateran University. From 1973–1990, Father Danylak served as a consultor to the Pontifical Commission for the Revision of Canon Law for the Eastern Churches.
In 1992, while serving as the rector of St. Josaphat Cathedral and chancellor of the eparchal chancery, he was appointed Apostolic administrator sede plena of the Ukrainian Catholic Eparchy of Toronto and titular bishop of Nyssa by Pope John Paul II. His appointment proved controversial, as the incumbent bishop, 81 year-old Isidore Borecky, refused to retire even though he had passed the mandatory retirement age of 75 established by canon law. It was also rumored that Bishop Borecky had requested a coadjutor or auxiliary bishop, not an administrator, and that Father Danylak had not been nominated for the position by the Ukrainian Synod. After six years of conflict between the two bishops, Bishop Lubomyr Husar, Apostolic administrator of Lviv, negotiated a resolution whereby Bishop Borecky retired and Bishop Danylak was reassigned to "special responsibilities in Rome", resulting in the vacancy of the Toronto eparchy effective June 24, 1998. Bishop Cornelius Pasichny of Saskatoon was appointed the new bishop on July 1 of that year.
During his retirement in Italy, Danylak supported certain claims by individuals to have seen visions of Jesus and Mary, claims about which the Holy See or the bishop holding responsibility as ordinary had expressed reservations or an explicitly negative judgement:
- The Garabandal apparitions
- Maria Valtorta's Poem of the Man God
- Alleged miracle in Naju, Korea
- "Bishop Roman Danylak". Catholic-Hierarchy.org. Retrieved 2007-04-13.
- Christopher Guly (January 3, 1993). "Vatican announces new appointments". The Ukrainian Weekly. p. 1. Retrieved 2009-07-29.
- Andrij Wynnyckyj (February 7, 1993). "Interview: The Vatican's administrator for Toronto eparchy". The Ukrainian Weekly. p. 3. Retrieved 2009-07-29.
- Andrij Wynnyckyj (January 31, 1993). "Furor erupts in Toronto Eparchy as Rome makes move against bishop". The Ukrainian Weekly. p. 1. Retrieved 2009-07-29.
- Andrij Kudla Wynnyckyj (July 19, 1998). "Toronto's Ukrainian Catholic Eparchy subjected to major reassignments". The Ukrainian Weekly. p. 1. Retrieved 2009-07-29.
- Letter by Bishop Danylak on "The Church and Garabandal"
- "Maria Valtorta, Her Life and Work" by Bishop Roman Danylak
- Testimonial letter of Bishop Danylak
- Letter of 13 February 2002 from Bishop Danylak
- Protest letter to EWTN
- Kwangju Archbishop Gives Directives On Naju Events
- Bishop Roman Danylak, "The Eucharistic Miracle of Naju (The Sacred Heart of the Divine Victim)"