Adelaide Archbishop Philip Wilson, who is the most senior Catholic official in the world charged with concealing child sexual abuse, has been found guilty of the offence in a NSW court.
Magistrate Robert Stone said Wilson failed to report to police the repeated abuse of two altar boys by pedophile priest James Fletcher in the NSW Hunter region in the 1970s.
The 67-year-old, who showed no emotion when found guilty at Newcastle Local Court on Tuesday, faces a maximum two years' jail.
Peter Creigh, a former altar boy who expected Wilson - an assistant priest at the time - to take action after he told him Fletcher repeatedly abused him when he was 10 in 1971, was a key witness in the landmark trial of Wilson.
Mr Creigh, close to tears after the verdict, said it was a "huge relief" and labelled it a "significant day for victims and their families".
Mr Stone accepted Mr Creigh and another altar boy told Wilson in 1976 that Fletcher had repeatedly abused them but the clergyman did nothing.
Fletcher was found guilty in December 2004 of nine counts of child sexual abuse. He died in jail of a stroke in January 2006.
The magistrate rejected claims by Wilson, who is suffering from the early stages of Alzheimer's disease, that he could not remember the altar boys telling him of the abuse in 1976.
Prosecutor Gareth Harrison told the court Wilson should be jailed to deter others from trying to protect the Catholic Church from abuse allegations.
In a statement released by the Catholic Church, Wilson said he was "disappointed" by the guilty verdict.
Sentencing is due to start on June 19.