Hamline studied for the ministry, but afterward studied law, and practiced for a while in Ohio. He became a preacher in the Methodist church in 1830. In 1844, when the Methodist church divided over slavery, he was a member of the General Conference, the church's legislative body, and drew up the plan of separation.
He provided US$25,000 of his own money to launch a school, which became Hamline University. A statue of the bishop, sculpted by the late Professor of Art Michael Price, stands on campus.