A member of the
Democratic Party, McKenna was elected to the Pittsburgh city council in 1875, and served as an alderman for the city's Fourth Ward. In 1888, he was appointed as a police magistrate. In 1893, he launched a successful bid to become mayor. His administration oversaw the completion of the
Highland Park Zoo; the
Carnegie Library's main branch was also completed during his time in office. On September 12, 1894, he addressed a crowd of former
Union Army soldiers, in his capacity as Pittsburgh's mayor, during the opening of the twenty-eighth National Encampment of the
Grand Army of the Republic, which was held at Pittsburgh's Grand Opera House. On December 29, 1895, he delivered a welcome address to the members of the Pennsylvania State Music Teachers Association during the opening of their annual convention, which was held that year at Pittsburgh's
Carnegie Music Hall. On New Year's Day in 1896,
Andrew Carnegie announced that he was appointing McKenna to serve as one of the thirty-six members of the newly created board of trustees of the Carnegie Art Gallery Fund. Also named to the first board were prominent Pittsburgh civic leaders
William Jacob Holland and the Rev. Dr.
Andrew Arnold Lambing. Following his tenure as mayor, he was appointed and re-appointed as police magistrate of the city's First Ward by his immediate successors, Mayors
Henry P. Ford,
William J. Diehl,
Adam M. Brown, and
Joseph O. Brown, serving in that capacity from 1896 to 1903. In 1893, McKenna and his wife moved to a home on Howe Street in Pittsburgh's Twentieth Ward. ==Death, funeral and interment==