John Wessels was born in Eagle Grove, Iowa on September 21, 1930 to John Henry and Barbara Muenzer Wessels. He was one of eight children. The Catholic school of Eagle Grove was staffed by the Sinsinawa Dominican Sisters and the town had a history of many vocations to the Dominican Friars. John's vocation to the Order was nourished by this rich Dominican tradition in the town. After doing two years of college studies in Dubuque, Iowa, at Loras College he entered the Order. He made his novitiate at St. Peter Martyr Priory in Winona, Minnesota and was given the name Cletus. He made his profession of vows on August 31, 1951 and was immediately transferred to the Dominican House of Studies in River Forest, Illinois where obtained a Master of Arts degree in philosophy. He continued his studies for the priesthood at St. Rose of Lima Priory in Dubuque and was ordained on May 25, 1957.

After ordination, he was sent to Rome to study at the Angelicum where he received the S.T.Lr. and S.T.L. degrees in 1959. He returned to St Rose Priory in Dubuque to teach at Mount Saint Bernard Seminary and was Dean of Studies. In 1962, he was sent to the University of Ottawa, in Ottawa, Canada, to complete his doctoral studies. He received the S.T.D and Ph.D. degrees in 1963. Returning to Dubuque as a Professor of Theology at the Aquinas Institute, he served as Associate Dean (1966-1968), Academic Dean (1968-1972) and third President of Aquinas Institute of Theology from 1972-1978. During his tenure as President the Institute expanded its mission to include new areas of ministry and continuing formation.

In 1978, he moved to Adrian, Michigan, where he was the Associate Director Weber Center. In 1981, he would move to Aquinas College in Grand Rapids, Michigan, to teach theology and work in campus ministry. During this time, he became increasingly interested in issues of social justice and human rights. For one year, he worked at the Quixote Center in Hyattsville, Maryland. The Provincial noting the needs of the province, asked him to accept the pastorate at Saint Albert the Great Parish in Minneapolis, Minnesota. From 1988 to 1997, he served as pastor during which time he had the difficult task of closing the parish school due to low enrollment. He implemented a major renovation of the parish church to encourage greater participation in the liturgy.

When his term as pastor ended, he embraced full time preaching and writing ministry. He worked with small reflection groups to review and refine his theological ideas. At the same time he served as Prior of the community at Saint Albert the Great Priory. In the final years of his life he published two books, namely; Jesus in the New Universe Story and The Holy Web: Church in the New Universe Story.

A few years before his death, he became aware that he was having problems with memory and speaking. For this reason he reluctantly had to retire from ministry. During the last year of his life he was not able to live with the Dominican community and moved to Providence Place in Minneapolis where he could receive the care he increasingly needed. On August 12, 2009, he died in the company of his brothers. The Mass of Christian Burial was celebrated at Saint Albert the Great Parish and was buried in the Dominican Plot at St. Mary's Cemetery in Minneapolis, Minnesota.