He joined the North Indiana Conference of the Methodist Episcopal Church in 1856. Those days were still pioneer, and he entered gladly into the sacrificial ministry of that period. It is a singular coincidence that he was doubtless the first minister of his faith to begin work near Union City, where he closed his earthly labors. It was his privilege, also, to build the first Methodist Episcopal church in the city where he died. The history of his ministry shows that he served all classes of charges--country, city, village, county seat. Several times the record is dotted with the word "Mission," which would indicate that he frequently followed the apostolic fashion of building strictly on his own foundations. He came to a place of leadership in his own Conference. To the day of his death he was an influential factor in all its plans and programs. Though he had been technically "superannuated" for sixteen years prior to his death, his mind kept its full vigor, and his word kept its full weight. Twice he was elected a reserve delegate to the General Conference, while in 1880 he was chosen as one of the regular delegates. From the beginning of his ministry Dr. Mendenhall showed the signs of a remarkable mind, and at the end of his ministry he was still manifesting a keen interest in current questions and in theological problems. His library to the last was freshened by the purchase of new books. When he turned his many volumes over to Gammon Theological Seminary that institution did not receive hundreds of antiquated volumes, but rather a collection brought down to date and selected by a master judgment. The intellectual, though suffused at times by a proper and restrained emotion, was his noticeable characteristic. He was given to thorough analysis. He was markedly painstaking. Records that he made of the conduct of his public services indicate that the final details were all regarded, and that hymns and Scripture lessons were chosen with a view to their bearing on the instruction of the day. Being a vigorous personality, he held his views with strength. He was keenly loyal to his convictions, whether these related to methods of work or to statements of doctrine. In his advocacy or in his antagonism he was always frank and open. His opponent could see him standing out in plain view, with no effort to protect himself by secrecy. Men could never doubt his sincerity, however much they might question the correctness of his positions. He knew no sinuous paths. He was as direct as sunlight, and he traveled in straight lines.