Dublin University is a university constituency in Ireland, which elects three senators to Seanad Éireann, the senate of the Oireachtas (the legislature of Ireland). Its electorate comprises the undergraduate scholars and graduates of the University of Dublin, whose sole constituent college is Trinity College Dublin, so it is often also referred to as the Trinity College constituency. Between 1613 and 1937 it elected MPs or TDs to a series of representative legislative bodies.

When James I first convened the Parliament of Ireland, the University of Dublin was given two MPs, elected by the Provost, Fellows and Scholars of Trinity College. It was not represented among the 30 Irish MPs which were part of the Protectorate Parliament during the Commonwealth of England, Scotland and Ireland.

Party organisations were not persistent during this time period, and have been added where appropriate. Among the MPs for the university in this period was John FitzGibbon, who later as Lord Chancellor of Ireland played a key role in the passage of the Acts of Union 1800, which merged the Kingdom of Ireland with the Kingdom of Great Britain to create the United Kingdom of Great Britain and Ireland.

The Acts of Union 1800 merged the Parliament of Ireland with the Parliament of Great Britain, to form the Parliament of the United Kingdom. The 300 seats in the Irish House of Commons were reduced to 100 Irish members in the House of Commons of the United Kingdom. The union took effect on 1 January 1801. The University of Dublin had one seat in this Parliament. There was no new election for the First Parliament of the United Kingdom: for constituencies like the University of Dublin which were reduced to one MP, they were chosen by lot, in this instance, George Knox.

In the Representation of the People (Ireland) Act 1832, the university was given a second seat in Parliament, elected by plurality-at-large, and the franchise was extended to all those with a Master of Arts degree. At this stage, there were 2,073 voters on the register. Plural voting, by those who held a vote in the university constituency and also in a geographical one, was allowed and prevalent.

A Topographical Directory of Ireland, published in 1837, describes the parliamentary history of the university.

By charter of James I. the university returned two members to the Irish parliament till the Union; after which time it returned only one member to the Imperial parliament, till the recent Reform act, since which it has returned two. The right of election, which was originally vested solely in the provost, fellows, and scholars, has, by the same act, been extended to all members of the age of 21 years, who had obtained, or should hereafter obtain, a fellowship, scholarship, or the degree of Master of Arts, and whose names should be on the college books : members thus qualified, who had removed their names from the books, were allowed six months to restore them, on paying a fee of £2, and such as continued their names, merely to qualify them to vote, pay annually to the college the sum of £1, or a composition of £5 in lieu of annual payment. The number of names restored under this provision was 3005, and at present the constituency amounts to 3135. The provost is the returning officer.

The Representation of the People Act 1918 extended the electorate to include all male graduates and scholars over the age of 21 and all female graduates and scholars over the age of 30, to be elected by single transferable vote. There were 4,541 voters registered for the 1918 general election. Plural voting continued to be allowed.

During the period of the Union between Ireland and Great Britain, the constituency predominantly elected Tory, Conservative and Unionist MPs, including Edward Gibson, who was later (as Lord Ashbourne) responsible for the Purchase of Land (Ireland) Act 1885, and Edward Carson, who led the Irish Unionist Alliance.

Dublin University was represented in the House of Commons until the dissolution of Parliament on 26 October 1922, shortly before the establishment of the Irish Free State became a dominion on 6 December 1922.

The Government of Ireland Act 1920 established a devolved home rule legislature, within the United Kingdom, for twenty-six Irish counties which were designated Southern Ireland.

Dublin University was given four seats in the House of Commons of Southern Ireland. The seats were filled by Independent Unionist MPs who were returned unopposed. They were the only MPs who attended the abortive first meeting of the House. After the signing of the Anglo-Irish Treaty, the four MPs met with the Pro-Treaty members of the Second Dáil to ratify the Treaty. The Parliament was formally dissolved as part of the arrangements under the Treaty and the establishment of the Irish Free State on 6 December 1922.

Sinn Féin contested the 1918 Westminster election on the basis that they would not take seats in the United Kingdom Parliament but would establish a revolutionary assembly in Dublin.

The university was entitled to return two Teachtaí Dála (known in English as Deputies and abbreviated as TDs) in 1918 to serve in the Irish Republic's First Dáil. This revolutionary body assembled on 21 January 1919.

In republican theory every MP elected in Ireland, including the two Unionist MPs from Dublin University, was a member of the First Dáil. In practice only Sinn Féin members participated.

The First Dáil passed a motion at its last meeting on 10 May 1921, the first three parts of which make explicit the republican view:

1. That the Parliamentary elections which are to take place during the present month be regarded as elections to Dáil Éireann.
2. That all deputies duly returned at these elections be regarded as members of Dáil Éireann and allowed to take their seats on subscribing to the proposed Oath of Allegiance.
3. That the present Dáil dissolve automatically as soon as the new body has been summoned by the President and called to order.

The Second Dáil first met on 16 August 1921, thereby dissolving the First Dáil.

Sinn Féin used the polls for the Northern Ireland House of Commons and the House of Commons of Southern Ireland as an election for the Irish Republic's Second Dáil. No actual voting was necessary in Southern Ireland as all the seats were filled by unopposed returns. Except for this university all other constituencies elected Sinn Féin TDs. The university elected four Independent Unionist members unopposed. As with the First Dáil, those Deputies could have joined the Dáil if they chose.

The Third Dáil elected in 1922 was, in United Kingdom law, the constituent assembly for the Irish Free State. From this time the Dáil represented only the twenty-six Irish counties and not the six counties of Northern Ireland. Non-Sinn Féin Deputies, including those from the university, began to participate in the Dáil.

In the Electoral Act 1923, the Irish Free State defined its own Dáil constituencies. The University of Dublin was granted three seats, to be elected by single transferable vote by all graduates and scholars, regardless of sex, over the age of 21. Plural voting was not allowed.

The Constitution (Amendment No. 23) Act 1936, removed the provisions in Constitution of the Irish Free State for University representation in Dáil Éireann, with effect from the next dissolution of the Oireachtas, which took place on 14 June 1937. Voters resident in the State had their Dáil registration switched to the geographical constituency of their registered address.^[2]

Note: The columns in this table are used only for presentational purposes, and no significance should be attached to the order of columns. For details of the order in which seats were won at each election, see the detailed results of that election.

Article 18.4 of the Constitution of Ireland adopted in 1937, provided that the university would have three seats in the new Seanad Éireann. The Seanad Electoral (University Members) Act 1937 gave effect to the constitutional provision, and provided that they would be elected by single transferable vote. The first Seanad election took place in 1938, and thereafter elections to the Seanad take place within 90 days of the dissolution of the Dáil. The Seventh Amendment of the Constitution, adopted in 1979, allows for a redistribution of the six university seats among the University of Dublin, the National University of Ireland, and any other institutions of higher education in the State which do not have representation.^[3]

Under the Seanad Electoral (University Members) (Amendment) Act 2024, the 2025 Seanad election to the 27th Seanad will be the last general election for the National University and the Dublin University constituencies. Polls for this election will close on 29 January 2025. At any Seanad general election held after 31 March 2025, they will be substituted by a new six-seat Higher Education constituency, enfranchising graduates from all institutions of higher education recognised under the Higher Education Act 2022. If a vacancy occurs during the 27th Seanad in the Dublin University constituency, the electorate will be Dublin University graduates on the Higher Education constituency register of electors.^[4]

The electorate is Irish citizens who have received a degree from the university, or undergraduates who have been awarded a foundation scholarship or non-foundation scholarship at Trinity College.^[5] After the Fourth Amendment in 1972, the age of eligibility was lowered from 21 to 18.^[6] Voting for the Seanad is distinct from that for the Dáil, so it is not considered plural voting; however, plural voting is possible for those who have received degrees from both the University of Dublin and the National University of Ireland. Trinity College Dublin is the sole constituent college of the University of Dublin, so the electorate is predominantly composed of graduates of Trinity; however, from 1975 to 1998, the University of Dublin also awarded the degrees of graduates at the Dublin Institute of Technology.

Nominations are by electors in their personal capacity; unlike Dáil elections, there is no provision for nomination by parties.^[7] Most of the senators for the constituency have campaigned as Independents, though Mary Robinson and Ivana Bacik took the Labour Party whip for periods of their time in the Seanad.

A number of the senators have had a reputation as being quite socially liberal, including Owen Sheehy-Skeffington, Noël Browne, and Catherine McGuinness. Three Senators were later appointed to the Supreme Court: T. C. Kingsmill Moore, Gardner Budd and Catherine McGuinness. Mary Robinson, first elected in 1969, was later elected as President of Ireland in 1990. In 1987, David Norris became the first openly gay member of either house of the Oireachtas. The senators have often included current or recent academics within Trinity College, such as professor of Latin and provost Ernest Alton, professor of Greek William Bedell Stanford, professor of mathematics Trevor West, professor of medicine Mary Henry, Ivana Bacik in law, and David Norris in English.

Note: The columns in this table are used only for presentational purposes, and no significance should be attached to the order of columns.

From 1832 (when registers of electors were first prepared) a turnout figure is given, for the percentage of the registered electors who voted. If the number of registered electors eligible to take part in a contested election is unknown, then the last known electorate figure is used to calculate an estimated turnout. If the numbers of registered electors and electors taking part in the poll are known, an exact turnout figure is calculated. In two member bloc vote elections (in which an elector could cast one or two votes as he chose), where the exact number of electors participating is unknown, an estimated turnout figure is given. This is calculated by dividing the total number of votes cast by two. To the extent that electors used only one of their votes the estimated turnout figure is an underestimate.

In 2011 Karin Dubsky, who was listed on the printed ballot papers, discovered after their distribution that she was not an Irish citizen and thus ineligible, and advised electors not to vote for her.^[17] The returning officer ruled that ballots giving her a first preference would be excluded, but ballots giving her a lower preference would be transferred to the next lower preference when relevant.^[18]

Following the resignation of Conor Cruise O'Brien on 13 June 1979.^[29][30]

Following the death of William Fearon on 27 December 1959.^[33][34]

• Caused by Samuels' appointment to the High Court of Justice in Ireland.

This was the last UK Parliament election held in the 26 counties which became the Irish Free State.

Note: The Times edition of 23 December 1918 reported that the Provost of the University, as returning officer, did not announce the figures. It was ascertained that Woods had 1,094 votes when elected. The above is the best reconstruction of the later counts which is possible with the available information.

• Caused by Samuels' appointment as Solicitor-General for Ireland.

• Caused by Campbell's appointment as Lord Chief Justice of Ireland.

• Caused by Campbell's appointment as Attorney-General for Ireland.

• Caused by Lecky's resignation.

• Caused by Carson's appointment as Solicitor General for England and Wales.

• Caused by Plunket's succession to the peerage, becoming Baron Rathmore.

• Caused by Madden's appointment as Solicitor-General for Ireland.

• Caused by Holmes' appointment as a judge.

• Caused by Plunket's appointment as First Commissioner of Works, and Holmes' appointment as Attorney-General for Ireland.

• Caused by Plunket's appointment as First Commissioner of Works, and Gibson's appointment as Lord Chancellor of Ireland, becoming Baron Ashbourne.

• Caused by Gibson's appointment as Solicitor-General for Ireland.

• Caused by Plunket's appointment as Solicitor-General for Ireland.

• Caused by Ball's appointment as Lord Chancellor of Ireland.

• Caused by Ball's appointment as Solicitor-General for Ireland.

• Caused by Lefroy's resignation.

• Caused by Chatterton's appointment as Vice-Chancellor of Ireland.

• Caused by Chatterton's appointment as Attorney-General for Ireland.

• Caused by Walsh's appointment as Master of the Rolls in Ireland

• Caused by Whiteside's appointment as Lord Chief Justice of Ireland

• Caused by Hamilton's resignation.

• Caused by Napier's appointment as Lord Chancellor of Ireland.

• Caused by Napier's appointment as Attorney-General for Ireland.

• Caused by Shaw's resignation.

• Caused by Jackson's appointment as Justice of the Court of Common Pleas in Ireland.

• Caused by Lefroy's appointment as Baron of the Court of Exchequer in Ireland.

• The constituency gained a second seat at the 1832 general election under the Representation of the People (Ireland) Act 1832.