Monsignor William Lynn is the first U.S. church official to face trial for his handling of sex abuse complaints.
An assistant restaurant manager has become the 12th juror seated in the landmark case about how the Archdiocese of Philadelphia dealt with priests accused of molesting children.
The jury of six men and six women are expected to hear evidence for about four months.
Ten alternates will also sit through the trial.
Monsignor William Lynn is accused of endangering children by transferring two accused priests to new parishes during the 1990s. The 61-year-old Lynn has pleaded not guilty and blames the late Cardinal Anthony Bevilacqua for hiding the problem.
The Rev. James Brennan and defrocked priest Edward Avery are charged with rape.
Brennan seems to be enjoying the jury selection process, frequently laughing along with lawyers. Lynn has been mostly somber.
Testimony is set to start March 26.