The church's teaching on marriage is unequivocal, it is uniquely, the union of a man and a woman and it is wrong that governments, politicians or parliaments should seek to alter or destroy that reality.

Initially serving as curate at Holy Cross Edinburgh from 1965 until 1966 he completed his teacher training certificate at Moray House College of Education. According to the BBC a source within the church said that O'Brien "doesn't know who his accusers are and doesn't know what they're accusing him of". On 24 February 2013 he failed to attend a special service to celebrate the eight-year tenure of Pope Benedict XVI at St Mary's Cathedral Edinburgh.

The announcement of his resignation followed allegations of inappropriate conduct with junior clergy. It was also announced that he would not be voting in the conclave to elect Benedict XVI's successor. On 3 March 2013 O'Brien admitted that his sexual conduct had at times "fallen beneath the standards expected of [him]".