Holy Cross College (also known as Clonliffe College), located in Clonliffe Road, Drumcondra was founded in 1854 as the Catholic diocesan seminary for Dublin by Cardinal Paul Cullen (1803–78)

The College was founded in 1854 by the then Archbishop of Dublin Paul Cullen, to provide priests for the Dublin diocese. In 1861 Rector of the Catholic University Dr Bartholomew Woodlock tried to secure land in Clonliffe west to build a new Catholic University, however this plan was shelved due to the expansion of the Railway line.[2] Plans were drawn up by the Architect James Joseph McCarthy for the proposed new University, McCarthy a famous architect designed the college building.

Following the 1879 University Education (Ireland) Act which incorporated the Royal University of Ireland, the Catholic University of Ireland was reconstituted as to comprise all Catholic Colleges including Holy Cross College, Clonliffe. Students would sit exams for the Royal University. Since the royal university was prohibited in awarding degrees in theology, the Catholic University would confer degrees in theology and divinity, such as BD and DD. Between 1881 and 1908 some 81 Clonliffe students graduated with a BA from the Royal University of Ireland.

Following the foundation of the National University of Ireland in 1908, Clonliffes seminarians would have also taken studies in University College Dublin and many walked in procession between Clonliffe and Earlsfort Terrace, prior to it moving out to Belfield.

In 1882 the Catholic University of Irelands Library (excluding medical books) was transferred from what became University College Dublin to Clonliffe.

In 1965 Holy Cross College, Clonliffe, the Dublin Diocesan Major Seminary, had been granted power to confer some of the Degrees of the Angelicum University of Rome, students would be award degrees such as BD or STB from the Angelicum.

For many years two students from the Vincentian would study at Clonliffe so as to have to opportunity to also gain a degree from UCD, there was a strong relationship between the Diocesan College and the Vincentian order, in that some Vincentian priests from the nearby St. Patrick's Training College and All Hallows would have lectured in Clonliffe. The connection with the Vincentians pre-dated Clonliffe in that students for the Dublin Diocese before the foundation of the College would have initially studied with the Vincentians in Castleknock College before completing their studies in Maynooth College.

The National University of Ireland, Maynooth validated a number of diplomas and certificates conducted in Clonliffe over the years.

In 2001 saw the seminary duties suspended due to a fall in vocations, with students for the priesthood for the diocese being transferred to national seminary in St Patrick's College, Maynooth.

The College is adjacent to the residence of the Archbishop of Dublin, just north of Croke Park Stadium. Clonliffe is the administrative headquarters of the Catholic Archdiocese of Dublin, and is used for retreats, conferences, meetings and courses. The Mater Dei Institute of Education College of Education was established in 1966 on part of the Clonliffe College campus, uses some of the resources of the former seminary such as the Sports grounds. A number of Dublin Diocesan bodies are based in Clonliffe College such as Crosscare which is located in the Red building. The Drug Awareness Programme, Crosscare, Clonliffe College, run the Certificate in Addiction Studies, from NUI Maynooth.

2015 sees the Pathways - Exploring Faith and Ministry adult education course, previously run for 30 years by the nearby All Hallows College, transferred to the Diocesan Centre and delivered in Clonliffe.