Father Merz was born in Milwaukee, Wisconsin on April 19, 1931. He graduated from Marquette University High School before entering the Society at St. Stanislaus Seminary, Florissant, Missouri on August 15, 1948. He was ordained at the Church of the Gesu in Milwaukee on June 15, 1961, and pronounced final vows at the Emmaus Center in Des Moines, Iowa on January 5, 1977.
Before ordination, Father Merz earned a bachelor's degree in philosophy (1954) and a master's degree in education (1955) from Saint Louis University. After ordination, he earned a bachelor's degree in sacred theology (1963) and a master's degree in spiritual theology (1973) from Saint Louis University. Father Merz also earned a master's degree in psychology from Gonzaga University (1964).
Upon completing the usual Jesuit course of studies at St. Stanislaus, Saint Louis University, and Saint Mary's College, Father Merz did regency at St. Francis Mission in South Dakota (1955-1958). After ordination (and further studies), Father Merz taught theology at Campion Jesuit High School in Prairie du Chien, Wisconsin for one year (1964-1965) before becoming a spiritual director for scholastics at Fusz Memorial (1965-1974). He then moved to Des Moines, Iowa where, with the exception of a sabbatical in 1979, Father Merz was missioned to the Emmaus Center for almost a decade. At the Emmaus Center, he was superior of the Jesuit community and director of pastoral renewal for the Diocese of Des Moines (1974-1979). After his sabbatical, he was director of the Wisconsin Province Renewal, the first Jesuit province 19th Annotation Retreat (1980-1983). Father Merz then used his gifts in Ignatian spirituality and cura personalis as master of novices for the Jesuit Novitiate in Saint Paul, Minnesota (1983-1991).
In 1991, Father Merz returned to his hometown where he spent the rest of his life. After a well-earned sabbatical (1991-1992), he was the Wisconsin Province Director of Pastoral, Retreat, and Native American Ministries (1992-1994) before being rector of the Marquette University Jesuit Community and working at the Center for Ignatian spirituality (1994-2000). After a sabbatical, Father Merz was the associate director of the Center for Ignatian spirituality (2001-2005). In 2005, he became the guestmaster of Arrupe House Jesuit Community and was a spiritual and retreat director (2005-2019).
Father Merz's ministry touched the minds, hearts, and spirits of priests, religious, and lay women and men throughout the world with Ignatian spirituality. He reached people through prison ministry, Native American ministry, Jesuit formation ministry, diocesan renewal programs, Jesuit renewal ministry, Jesuit higher education, international retreats, directed retreats, preached retreats, and spiritual direction.
Father Merz also shared Ignatian spirituality with countless people through the books he authored. His writings include Moment by Moment; Moments to Remember: Ignatian Wisdom for Aging; A Pathway to God; and Finding God in Each Moment: The Practice of Discernment in Everyday Life.