When an endowed priesthood holder violates the law of chastity before he is married, what church discipline is invoked and what is it based upon (severity, length of time, etc)?
The duties of a Bishop was given by revelation to Joseph Smith and recorded in Doctrine & Covenants 107:
“68 …. for the office of a bishop is in administering all temporal things;
69 Nevertheless a bishop must be chosen from the High Priesthood, unless he is a literal descendant of Aaron; ….
72 And also to be a judge in Israel, to do the business of the church, to sit in judgment upon transgressors upon testimony as it shall be laid before him according to the laws, by the assistance of his counselors, whom he has chosen or will choose among the elders of the church.”
To be a “Common Judge in Israel” is one of the Bishop’s greatest responsibilities. He is to protect the Church and help the members of his congregation gain forgiveness of their sins. He has been given the spirit of discernment to help him with this great responsibility.
Each of us need to confess all of our sins to the Lord, as only He can forgive us. Commission of serious sins, especially those of a moral nature such as the one you speak of, also needs to be confessed to the Lord’s representative under whose ecclesiastical jurisdiction one lives. In most cases this would be their Bishop. It is the Bishop’s responsibility to determine what course of action needs to be taken to protect the Church and assist the individual in repenting of his sins and gaining forgiveness from the Lord.
If any discipline is needed, it would be primarily the Bishop who would determine what needed to be done. He would consider many factors, including those that you mentioned, whether the individual freely confesses his sins or if he has to be confronted in order for him to confess. Other factors would be how widespread knowledge of the sin is, the effect it has had on those involved, and whether the individual was serving in a leadership capacity in the Church when the sin was committed. The promptings of the Spirit will be his greatest help in determining the course of action to be followed.
The following statement appears in the Church’s website concerning the discipline of those who have committed transgressions. “Bishops and branch presidents and stake, mission, and district presidents have a responsibility to help members overcome transgression through repentance. The most serious transgressions, such as serious violations of civil law, spouse abuse, child abuse, adultery, fornication, rape, and incest, often require formal Church discipline. Formal Church discipline may include restriction of Church membership privileges or loss of Church membership.”