Before the merger was consummated, however, Horton had resigned his position as CC executive to assume the position of dean of the Harvard Divinity School, in 1955. The Rev. Fred Hoskins succeeded Horton as the final CC minister and general secretary; he became one of the first co-ministers of the new UCC. At Harvard, Horton expanded upon his inter-church interests, bringing new programs to the school such as religious studies and a chair in Roman Catholic theology. A one-time moderator of the International Congregational Council, Horton took on the leadership mantle of the WCC's Faith and Order Commission beginning in 1957. It was from that vantage point that Horton was invited to observe the Second Vatican Council; he compiled material for a four-volume journal of the proceedings.