Collier served as minister of the North Olmsted United Methodist Church in North Olmsted, Ohio He began his career with Baldwin-Wallace College in 1974 as college chaplain and Professor of Religion. He was appointed Associate Dean of Academics and director of the college's Mission Action Project. In 1981, Collier became Dean of the College upon Neal Malicky's elevation to college president. Collier was appointed President of Baldwin-Wallace in 1999, following Malicky's retirement.
During his presidency Collier oversaw the renovation of the BW rec center, residence halls, and overseeing a campus master plan that has led to many major renovations on campus such as Malicky hall being built. . Malicky Hall combines Baldwin Library and Carnegie Hall with an addition of new classrooms and offices. As well, during this time BW began to expanded and renovated residence halls and academic buildings. In addition, the college has purchased existing buildings in the Berea community for academic and student residential use. After 32 years of service, Collier retired from his presidency in June 2006. BW has named a lecture series called "Goals of Enduring Questions: The Mark Collier Lecture Series" named after Collier.