• Born in Adelaide, Bishop Greg O’Kelly was educated by the Josephite Sisters in St Peters Parish School, and then by the Jesuits at Saint Ignatius' College, Norwood. In 1959 he entered the Jesuit Order.
• University and Jesuit studies undertaken in Melbourne, where he also taught at Pentridge Prison and lectured at Christ’s College (Teachers’ College) in Melbourne.
• Ordained to the priesthood in St Ignatius Church, Norwood, 9 December 1972.
• In 1974 Appointed Assistant to the Jesuit Master of Novices in Sydney.
• In 1975 He returned to Adelaide and in 1978 was appointed Headmaster of Saint Ignatius' College, Adelaide.
• 1979 to 1981 Chairman of the South Australian Catholic Schools Commission.
• 1979 to 1981 Chairman of the Association of Catholic Secondary School Principals Association.
• 1982 He was transferred to become Headmaster of Saint Ignatius' College, Riverview, New South Wales. Headmaster 1982 to 1993.
• 1987 – 1988 Chairman of the Headmasters’ Conference of New South Wales.
• 1987 to 1989 Ministerial appointment to the Governing Council of Sydney College of Advanced Education.
• 1986 Chairman of the Board of the Guild Centre (Independent Schools).
• 1989 – 1990 Chairman of the Association of Independent Schools of Australia. Represented
• AHISA in the United Kingdom and South Africa.
• 1980-1990 Conducted many presentations of the Colloquium on the Ministry of Teaching – Australia, Philippines and Hong Kong.
• 1990 Nominated Fellow of the Australian College of Education.
• 1991 Nominated by Australian Rostrum, New South Wales, as Speaker of the Year.
• 1994-2006 Headmaster of Saint Ignatius' College, Adelaide.
• 1994 Awarded the Order of Australia in Queen’s Birthday Honours for ‘Services to Education’.
• 1996 Effected change of Saint Ignatius' College to include Junior Primary and full coeducation.
• 1996 to 2006 Two terms on Council of Priests for Adelaide Archdiocese.
• 2003 – 2006 Member of Consult for Jesuit Provincial, Australian Province.
• 2004 – 2006 Member of the College of Consultors for Archbishop of Adelaide.
• 2001-2006 Chairman of the Board, Sevenhill Jesuit Mission & Cellars Association Inc.
• 2006 – Thursday 14 September, Ordination as Auxiliary Bishop of Adelaide. First Jesuit Bishop in Australia.
• 2007 – Recipient of Alby Jones Award for meritorious educational leadership achievements and to perpetuate the memory of the life and work of Dr AW Jones and to recognise an educational leader whose achievements have shown exceptional merit in areas of major concern to Dr Jones.
• Installed as President of South Australian Council of Churches, 21 July 2007.

Bishop O’Kelly has made many presentations at various education conferences over the years, and has written numbers of articles, mainly on the formational aspects of education. He has also been involved in a series of talkback radio programmes on values, and other media interviews took place concerning young male Afghan asylum seekers in community detention.