O'Farrell returned to Ireland in 1903 and for the next ten years conducted missions and retreats based from the Vincentian Parish at Phibsboro, in Dublin.
His election was considered a surprise by some as O'Farrell had never served as a parish priest in Australia, nor held the office of Superior in his own community, or, it would seem, any administrative position other than that of Vice Rector at St John's.
[2] After an expansionist period under Bishop Dunne, O'Farrell is accredited with placing the diocese on a firm financial and administrative footing.
O'Farrell acquired Hathrop, a palatial residence in Bathurst and established St Vincent's Hospital in 1922 as "an institution catering especially for the sick poor.
O'Farrell is also credited with the growth of the Society of Saint Vincent de Paul in the diocese, with congregations at Bathurst, Portland, Orange, Wellington, Cowra, Mudgee, Canowindra, Gulgong, Coonamble and Dubbo.
When a summer school of teachers was organised by O'Farrell with attendees from the Department in Public Instruction, the Brothers made a cursory appearance.
Following the commissioning of a report that showed less than satisfactory education and teaching performance, O'Farrell charged the Brothers with incompetence and demanded in November 1924 that they leave the diocese.
[2] Aware that his health was failing, O'Farrell travelled to Rome for the Holy Year celebrations in 1925, taking his administrator, Father John Norton with him.