George Miller, 70, was a central figure in the controversial efforts by Los Angeles Cardinal Roger Mahony to deny prosecutors access to archdiocesan personnel files, the Los Angeles Times reported.
Miller pleaded guilty last month to molesting the boy, and also admitted he sexually abused at least three other boys, the newspaper said.
Prosecutors said Miller met the boy and his mother when the boy was 5 years old and Miller was assigned to Guardian Angel Church in Los Angeles.
"My family trusted you to teach me the ways of the Lord, not the ways of hell," a victim who is now in his 30s told Miller in court Friday.
Miller's attorney said after the court session the former priest had decided not to contest the charges against him, even though his version of the events was different.
Prosecutors had charged Miller in 2002 with molesting several boys but those charges were eventually dismissed -- along with charges against other priests or former priests -- after the U.S. Supreme Court found unconstitutional a California law extending the statute of limitations in some sexual abuse cases.
The case from 1988 and 1989 allowed authorities to revive the prosecution of Miller, who was removed from the priesthood in 2005. Lawyers for the victims in the case said Miller had been placed on leave in 1996 after a third accusation of molestation against him, the Times reported.