He entered St. Andrew’s College, Drygrange to study for the priesthood and was ordained on 3rd April 1965 in St Mary’s Cathedral, Edinburgh by the then Archbishop Gordon Joseph Gray.

Cardinal O’Brien has held appointments as a priest at Holy Cross Edinburgh, Our Lady’s and St Bride’s Cowdenbeath before coming here to St Patrick's Kilsyth.

Upon the retireal of Canon Thomas McGarvey, Fr Denis O'Connell was appointed as Parish Priest of St Patrick's Kilsyth and started on the same day, Wednesday 9th February 1971(see Kilsyth Chronicle article below), as his new assistant Priest, Fr Keith Patrick O'Brien.

Fr. O'Brien quickly set to work in this large and busy Parish most notably being involved in the establishment of a new Convent in Kilsyth for the Franciscan Sisters of the Immaculate Conception in May 1972. Througout his tenure in Kilsyth Fr O'Brien was involved not only in his pastoral work as a Parish Priest but also in his associations with the many clubs and associations which used St Patrick's Halls which helped him to become known in the wider community of Kisyth. At this time in St Patrick's pastoral life was noted for the upsurge in House Masses where virtually every Catholic family in the town had Mass said in their own home. At the same time there was great devotion to the 'Living Rosary' and also support for the cause for the Beatification of at that time the Blessed (now Venerable) Margaret Sinclair.

St Patrick’s Newsletter 20th Oct 1974
Diocesan Changes - Father O’Brien’s Transfer to Bathgate.
Fr O’Connell writes: “It is with sadness and a deep sense of personal loss, which I know will be shared by all our people, that I have to announce this morning the transfer of Fr O’Brien to Bathgate and to an assignment in St Mary’s Bathgate, one of the largest Secondary Schools in the Diocese – an assignment for which of course, Fr Keith is singularly suited with his teaching qualifications and with his considerable experience as a full time School Chaplin in Fife.
Need I say that he leaves with the prayerful good wishes of countless friends in Kilsyth as well as our most grateful appreciation of his outstanding priestly work in our Parish over the past 3 years.
As some degree of compensation and indeed a measure of Fr Keith’s worth, he is being replaced at St Patrick’s by two priests, now that the staffing situation has been eased slightly after the recent ordinations. We welcome Fr Robert McGarrigle from St Kentigern’s Edinburgh and Fr Brian Byrne from St Margaret’s Dunfermline.”

St Patrick’s Newsletter 20th Oct 1974
Fr O’Brien Writes

Dear Fr Denis,
As I try to gather my thoughts before leaving Kilsyth, my mind flashes back over the many projects in which we were involved. I think over the years we were together we did try to cater for all our people and try to bring them closer to God.
Would you please pass on my thanks to all the Parishioners of Kilsyth for all their many kindnesses to me. From the first moment of my arrival to the day of my departure, I have felt that I was a member of a very happy family and I have been very grateful for the way in which I have been welcomed by all the people.
I take this opportunity of thanking all those who have given me gifts before leaving and I know that you will also give me the greatest gift – that of remembrance in your prayers and in your Masses and Holy Communion.

Fr. O'Brien left St Patrick's Kilsyth on 25th October 1974 to take up a posting at St Mary’s Bathgate and as a teacher and chaplin at the local high school.

In 1977 he was appointed Spiritual Director to the student at St. Andrew’s College Drygrange and in 1980 was appointed Rector to St Mary’s College, Blairs, Aberdeen.

The announcement of his appointment to the See of St Andrew’s and Edinburgh was made on Monday 3rd June 1985. He is the 7th Archbishop of this ancient See since the ‘Restoration of the Hierarchy’ in 1878.

His Episcopal Ordination as Archbishop took place at St Mary’s Cathedral Edinburgh on 5th August 1985 where the principal Consecrator was his immediate predecessor His Eminence Gordon Joseph Cardinal Gray with co-consecrators of His Excellency Archbishop Bruno Heim Apostolic Pro Nuncio to Great Britain and Ireland and the then Most Reverend Archbishop Thomas J Winning of Glasgow later Cardinal Winning.

Pope John Paul II created Keith Patrick Archbishop cardinal priest, with the titles of Ss Joachim and Anne ad Tusculanum in Rome at St Peter’s Bascillica on 21 October 2003.

The Cardinal was made Bailiff Grand Cross of Honour and Devotion of the Sovereign Military Order of Malta in 2005; and appointed Grand Prior of the Scottish Lieutenancy of the Equestrian Order of the Holy Sepulchre of Jerusalem in 2001; and appointed Knight Grand Cross in 2003.

The Cardinal was awarded the Honorary Degree of Doctor of Laws from St Francis Xavier University, Antigonish, Nova Scotia, Canada in 2004; and awarded the Honorary Degree of Doctor of Divinity from the University of St Andrews in 2004; and the Honorary Degree of Doctor of Divinity from the University of Edinburgh also in 2004.

He was Apostolic Administrator of the Diocese of Argyll and the Isles from 1996 until 1999.

After his creation as Cardinal, Cardinal O’Brien was appointed a member of the Pontifical Council for Social Communications and also a member of the Pontifical Council for the Pastoral Care of Migrants and Itinerant People.

He is at present the President of the Bishops’ Conference of Scotland and fulfils various engagements outwith his own Archdiocese at the request of other members of the Bishops’ Conference.

As well as ministering in his own Archdiocese and elsewhere in Scotland, the Cardinal has always shown an intense interest in the missions, having visited initially the territory previously adopted by his own Archdiocese – Bauchi in Northern Nigeria on two occasions. He has also been with his priests on loan in Central America, having visited El Salvador on three occasions and Chiapas in Mexico on two occasions, as well as recently visiting one of his priests in Guatemala.

As a Director of the Scottish Catholic International Aid Fund (SCIAF), the Cardinal has visited projects funded from Scotland in successive years – visiting Rwanda and the Democratic Republic of the Congo in 2004, Ethiopia in 2005, and Darfur in the Sudan in 2006. He has also visited India early in 2007 and China in the latter part of 2007. In 2006 he visited various projects supported by Holy Rood High School and St John’s Parish, Portobello in the Diocese of Moshi in Tanzania.