The announcement comes after allegations by three priests and one ex-priest of inappropriate behaviour, published in yesterday's Observer newspaper and dating back to the 1980s. The cardinal reportedly contests the claims.
Cardinal O'Brien is no stranger to making the news but it is more usually the result of his at times outspoken views.
He has been an advocate of priests marrying but also an outspoken opponent of plans to legalise same-sex marriage.
Last year his stance earned him the Bigot of the Year award from the gay rights group Stonewall.
In 2007 he caused controversy when, speaking on the 40th anniversary of the Abortion Act, he said the termination rate north of the border was equivalent to "two Dunblane massacres a day".
In 2008 he described the implications of the Human Fertilisation and Embryology Bill as "grotesque" and akin to "Nazi-style experiments".
The 74-year-old, who is Archbishop of Saint Andrews and Edinburgh, was created and proclaimed a cardinal by Pope John Paul II in October 2003.
The cleric was born in Ballycastle, County Antrim, Northern Ireland.
He obtained a bachelor of science degree in chemistry and mathematics from the University of Edinburgh and a diploma in education.
On April 3 1965 he was ordained a priest.
Cardinal O'Brien served as assistant parish priest and as chaplain of St Columba Secondary School in Cowdenbeath, where he taught maths.
He was spiritual director of St Andrew's College in Drygrange and rector of St Mary's College, Blairs.
On August 5 1985 he was ordained Archbishop of St Andrews and Edinburgh.
Six years later he was awarded the Equestrian Order of the Holy Sepulchre of Jerusalem: Knight Commander with star.
From 1996 to 1999 he served as Apostolic Administrator of the Diocese of Argyll and The Isles and from March 2002 until 2012, Cardinal O'Brien was President of the Bishops' Conference of Scotland.
The cardinal had a pacemaker fitted in 2008 following heart problems and dizzy spells.