Kansfield served the Emmanuel Reformed Church, London, Ontario, as a student pastor, in 1964. From 1965 to 1968, he was the pastor of the Second Reformed Church of Astoria (Queens, NYC). While doing graduate study in Chicago, he served the First Reformed Church of Berwyn, in an interim between pastors, and the Ivanhoe Reformed Church of Riverdale as an associate pastor (1968–1970). From 1970 to 1983, Kansfield was the Librarian and a member of the faculty in Western Theological Seminary, Holland, MI. From 1983 to 1993, he was the Director of the Ambrose Swasey Library, and Associate Professor of Church History in the Colgate Rochester Divinity School/Bexley Hall/Crozer Theological Seminary. The Ambrose Swasey Library also served the St. Bernard's Institute. In 1993, Kansfield was called to serve as President and the John Henry Livingston Professor of Theology for New Brunswick Theological Seminary. The General Synod of the Reformed Church in America twice elected him to the ecclesiastical office of Professor of Theology, in 1982 (which he resigned in 1983) and in 1993. During his presidency, through the concerted work of many persons, the student body increased by more than 50% and became much more ethnically and socially diverse; the faculty grew by two positions, and the school's endowment was doubled.