Asa Mahan graduated from Hamilton College in 1824, and from Andover Theological Seminary in 1827. On November 10, 1829, he was ordained pastor of the Congregational church in Pittsford, New York, and in 1831 he was called to the pastorate of a Presbyterian church in Cincinnati, Ohio. He was a trustee of the new Lane Seminary, the only Lane administrator to vote in favor of the students' right to debate "immmediatism", setting all slaves free immediately, versus colonialism, sending them to Africa. When a majority of Lane's students resigned as a group (the Lane Rebels), to end up at Oberlin a year later (1835), he did as well. At the students' insistence he was appointed President of the newly-founded Oberlin Collegiate Institute, simultaneously serving as the chair of intellectual and moral philosophy (ethics) and professor of theology. The students also insisted, as a condition of their enrollment, that Oberlin admit students of all races, which Mahan's liberal views towards abolitionism and anti-slavery helped get the approval of the reluctant trustees. Oberlin was the second college to admit African Americans; the first was the Oneida Institute, a short-lived predecessor of Oberlin, which did not admit women.