In 1960, Tanner was called as an Assistant to the Quorum of the Twelve Apostles, a full-time LDS Church general authority. In the church, he preferred to be referred to as "N. Eldon Tanner." In 1962, the death of George Q. Morris created a vacancy in the Quorum of the Twelve Apostles, which Tanner was called to fill in October 1962. He was still the quorum's junior member one year later when he was called into the First Presidency as second counselor to church president David O. McKay. Tanner remained in this position for the presidency of Joseph Fielding Smith (1970–72), and then became first counselor to Smith's successor, Harold B. Lee, and later to Spencer W. Kimball until Tanner's death.