One of the Three Witnesses to the divine origin and truthfulness of the Book of Mormon. He financially helped Joseph Smith and the Church. The Lord asked Martin Harris to sell his property and give his funds to pay for the publication of the Book of Mormon (D&C 19:26–27, 34–35); to be an example unto the Church (D&C 58:35); and to help pay the costs of the ministry (D&C 104:26).
Martin Harris was excommunicated from the Church but later returned to full membership. To the end of his life he bore witness that he saw the angel Moroni and the gold plates from which Joseph Smith translated the Book of Mormon.