In 1967, Marianne O’Sullivan became the first paid employee in the Diocese of Brentwood. To begin with, she worked alone in a house that had been acquired as the headquarters for the new administration. She handled the finances at that time, but eventually the then bishop, Patrick Casey, asked her to be his secretary.

In those days, bishops’ secretaries were usually priests. O’Sullivan was among the first women to take this role. She went on to serve Bishop Casey’s successor, Thomas McMahon, for the whole of his 34-year episcopacy. She had a reputation for being super-efficient and utterly loyal to her bishop.